@AwardWell technically Splatoon IS an HP bar based game - that's where the data mining for weapons comes in. I.E. capping of bamboozler at 99, etc. I believe inklings have 100HP and the numbers play out accordingly.
Personally I think dmg up is fine, it's def up that I think breaks the game a little more. It's entirely ineffective against some weapons, but devastating on others, and because the game relies so much on "knowing how many hits it takes to kill" a player wearing def up can massively disrupt your ability to perform (whereas getting killed faster by def up doesn't leave the error on your own part. I know using octobrush one time against another octobrush with FULL dmg stacking left me almost useless. She was the best player in the lobby, S+, and even if I could match her in skill, I could not beat her because she could simply kill me faster in any even encounter. Nearly every weapon is made better by stacking EXCEPT ttk, which I believe is ALWAYS 3hko no matter what. But like you said, that's a problem. Even if you want to run different abilities, if the enemy might be wearing def up, then you NEED to run dmg up to be effective against them at all with most weapons (not ttk!

) It's too risky to not be able to counter def up, so it does end up coming down to everybody trying to stack as much of one or the other as possible "just in case" their opponent does the same, and nothing else gets play time. I personally prefer not using too much with a charger, and yet with all the def up I've been finding myself swapping out for all my dmg gear to counter....keeping the meta going. One special shoudl never require another special to counter it. Especially not a powerful one. But without it the slow ttk weapons would become useless.
Then again I've been experimenting with 2 QR mains on my octobrush INSTEAD of damage. Not sure which way I'll go. But getting back into the game fast does have some serious advantages. Especially solo when you have to carry :D
Actually, if I remember correctly, I don't think
any weapon's minimum hits-to-kill can be altered by Damage Up (supposedly). Weapons like Aerosprays, brushes, and Squelchers will
appear to kill quicker in many cases because their base damage (per flick/shot) is increased (so indirect hits/finishing hits can do more damage and splat sooner), but some of these can take so many hits to kill unbuffed that it doesn't feel unusual or imbalanced there. It's all of course continually effected by where the target is in relation to the hitbox, if each shot is a direct hit or not, etc. I really think that's where Damage Up shines most, in cases of indirect hits / "splatter" kills.
This quote from Inkipedia's article on Damage Up helped me understand the mechanic best: "For example, the
Aerospray MG has a base damage of 24.5, meaning that it takes five hits to splat an enemy
Inkling. The game will not allow the Aerospray to splat in less than five hits. Therefore, Damage Up will cap the Aerospray's damage at 24.9, so it will still take five hits to splat. This rule applies to all weapons that take more than one hit to splat and deal fixed damage."
True, Inklings technically have health bars of 100 HP, but this mechanic is so loosely incorporated in the meta, with the overwhelming abundance of 1-2HKO weapons (and those that kill so quickly they may as well be the same). Inkling health bars are never something truly modified or kept track of by the player. Basically, if you're hit, you in most cases need to defend aggressively or flee, because being hit once in Splatoon very often means you're either about to kill or be killed, or you're already dead lol. There's nothing wrong with this, it's part of what makes Splatoon exciting and fast-paced. But the existence of supposed "buffs" and terminology like Damage and Defense "Ups" give an impression that we as players actually have substantially modifiable health bars, damage output or layers of defense, and that really isn't what these abilities have added up to. It's more like "barely surviving that indirect hit" versus "being finished off by that indirect hit" lol.
That being said, yeah I agree it's a really tough call to make a statement like "just scrap Damage Up," because it gives benefit to certain weapons that honestly need it. It's true, maybe Defense Up is the real problem, because it just created this ability counter merry-go-round.
The thing about Damage Up is that, since people see it so often, everyone thinks it is good. While all the chargers/rollers/burst bombs/anti-defence up weapons make good use of it, I also see things like Damage Up on random shooters like N-Zaps and Splooshes, as well as tri sloshers, splatlings, and even the occasional .96 gal. It may be good, but it is not good on absolutely anything.
Another thing about the Dynamo's, you may only see them jump out from nowhere and engulf you in an inky wave of doom, yet they eat ink like crazy and the last nerf makes them wait a few moments before they start recovering ink (In my opinion, this is more annoying than the reduced one shot spread). Yes, they seem like crazy fast, powerful murder machines, but in reality, they are highly slow, inefficient, and crippled by lag that makes them fairer to use.
Yeah, as I said, Damage Up really only benefits certain weapons. Generally speaking, vanilla rollers, most Sloshers, and certain shooters will see very, very little benefit from it. The problem is, even though it supposedly can't effect hits-to-splat, when you're buffing the damage of already high-damage weapons, that can cause a very noticeable increase in indirect hit/"unintentional" splatter kills. If you've already treaded enemy ink for a second or two, and are then hit by one Damage Up Gal shot, chances are extremely high that tiny amount of chip damage was all you needed for that one Gal shot to become a 1HKO. This is part of the problem, that it can give imbalanced benefits to specific weapons, and basically nothing to others.
To chime in on the Dynamo conversation...it is a very frustrating issue to deal with, I've definitely been there myself (their Dynamo hitbox feeling different from yours). Honestly though I don't ordinarily have huge problems dealing with enemy Dynamos nowadays, not most of the time anyway. This is largely because it's probably the weapon I'm most familiar with in the game lol. I know its swings well enough to know when to close in quick, and when to stay the hell away. But...that definitely doesn't stop me from the occasional miscalculation, or outright mistakes lol. :p
Dynamos do indeed have a unique combination of range and 1HKO potential (that, in its pre-nerf form, was surely broken), but it isn't as devastating as some still assume. Its full range is absolutely not the full extent of its 1HKO radius. That's actually quite a bit smaller. A maximum distance Dynamo fling outranges even the Dual Squelcher...that piece of information puts a sour scowl on the face of many players unfamiliar with the weapon. But the thing is, if you're caught at the tail end or outer perimeters of that wave, you'll take barely any damage. Its kill potential is fearsome, no doubt about it, but it's ridiculously slow and still has trouble performing many roles that OU weapons like Gals and Tentateks can take on all day with ease. I also completely agree with you, honestly maybe the most devastating nerf to it was that horrible lag in ink refilling.

You're a big giant neon sign threat for 4 swings, then have to be a useless sitting duck for several moments. :p