Where would you suggest the right vantage points there are?
depends on how much caffeine is in your system
if you're twitching like a rabbit on crack cocaine, you can safely hold the first box on your opponent's walkway (the first one from mid, that is), which covers the mid drop-down and the opponents' left path. if you're a little less caffeinated, the closest box to your spawn on your own walkway is good for covering the opposite angle but you need to be very wary of what's going on in mid since you're further removed. and since dynamos are limited in where they can attack from, you can pretty easily pick them off from whatever angle they decide to take.
or if you're one of those weird people who do not measure your success with a charger as some function of the amount of coffee ingested prior, just base it on how confident you are in your aim and awareness.
alternatively if you aren't confident in your scope you can hold the mid dropdown or one of the corners, but that greatly limits your ability to block pushes or create picks
Okay, so obviously every single charger I ever played even in A rank lobbies that were themselves A+ was terrible at the game, oh man what are the odds ¯\_(ツ)_/¯
Of course if a dynamo player is dumb about it and just straight jumps at a charger fully frontal while making it clearly obvious he's trying a number in completely open terrain, he's going to get his brains blown out. No questions asked. Lived through it enough times. Splatoon doesn't exist in a vacuum though and bolting towards a charger who's first preoccupied with something else before they notice there's someone on the move will almost always result in them getting splatted because it will generally be too late for them. Using the terrain to your advantage, e.g. in terms of cover, also helps. The fact that the Dynamo creates a huge area of ink with a wide range means that one unnoticed flick is generally enough to create a large and outreaching approach path I can swim through, coupled with the fact that in a lot of instances the charger just shot somewhere else and needs to reload the weapon.
Also, listing your recorded reaction time is kind of misleading because that's only one aspect what goes through the process of seeing a target and hitting a target. a) the information arrives through internet latency of variable length from the enemy to your client, b) the charger needs to perceive through eyes and ears and the stimulus needs to be conducted to the central nervous system (eyes are generally slightly slower), c) they must cognize/recognize and evaluate the input in their CNS, d) coordinate a muscular reaction (best case scenario from muscle memory which would be slightly shorter than creating a new input program), e) conduct and execute the muscular reaction in the shape of button pressing from the antebrachial musculature inserting at the aponeuroses of the fingers and f) the performed input runs through the latency of the gamepad to the system (since the game handles deaths client side further latency is irrelevant). Your recording and frame count as I see it only covered aspect e) and f), unless you literally hooked yourself up with an EEG, EMG and ENG. In sum they would amount to way more than 100ms anyway.
A+ is a trench with the exploit & net positive rating adjustment at 50% win rate (since A- and A lower the overall rating on a team, making rating changes for A- and A more likely to be +12 or -8) pushing people toward A+, and a large percentage of A+ players simply not playing the game anymore. if the lobbies I've been in lately are any indication, A+ is no longer any guarantee of skill, just of patience. so yes, the odds are good that you have not played against a good charger yet. considering that I'm not a good charger and I've met very few people who can outplay me with their own charger, yeah, I'd bet on it.
not sure why you think that chargers not existing in a vacuum means dynamos don't either. a dynamo flicking paint is one of the loudest and least subtle things in the entire game, and its animation is almost as long as an e-litre's 100 damage charge time. if you don't somehow draw attention to yourself from any number of angles--especially on those maps you claim to specialise in--and get up close to a charger, either they or their team (probably both) are doing something seriously wrong. the first thing I do after taking a shot is make sure my position is secure. a giant puddle of enemy ink appearing in my periphery is a pretty good indication that a dynamo is somewhere close by, meaning I need to do something about it. and, hey, if I'm screwed, there's always the superjump, which also takes less time than your swinging animation.
as alluded to at the top of this post, a good charger can and does lock down multiple areas, usually from some sort of vantage point that renders them immune to all but the longest-range weapons. dynamos do not belong to this category. perhaps a dynamo can get close if the charger misses (which, as previously stated, they shouldn't), but the charger should not be sitting around waiting for people to flank them. furthermore a scope only needs one second to charge (e-liter needs about a second and a half for a 100 damage shot), which is only slightly longer than the dynamo's
point blank time to kill, and with a prepared shot, can kill the instant something enters its range.
even if your paragraph on reaction times were relevant (which we'll get to in a minute), jumping or really doing anything at all with a dynamo roller still gives me more than a second to react, aim, and shoot in the worst-case scenario.
I also did not mention reaction time. yes, reaction times are on average quite a lot slower than 100ms (last time I tested mine it was around 190ms but that was a few years ago), and that's kind of the point. predicting when and where stimuli will appear reduces the amount of time needed to react to them. if you know a pitcher is going to be throwing a curveball, you can start reacting to it before the ball has left their hand. in the same sense, if I know someone is likely to be coming around a corner at a given moment, or if I see someone jump, I can set up a shot well before I even know precisely where they are and drastically reduce my "reaction" time as a result (which is the entire reason peeking is so effective; see CS:GO AWP users).
EDIT: removed some of the snark in the last few paragraphs. sorted out in PM, much respect to
@Grafkarpador for doing so