This is the most helpful Splatoon guide I have read, and is especially useful seeing as my gaming background generally excludes any kind of shooter. I actually created an account here just so I could leave you with some feedback.
I think the guide's greatest strength is that it helps a player improve their game regardless of their playstyle, weapon of choice, or mode of play. However, I think that its focus on the individual player is also its largest shortcoming. While an MVP can certainly aid in securing victory, one player alone will not win you the match. As many of us have undoubtedly experienced, being down just one player makes it very difficult to pull off a win.
You do mention near the end of section VI how your team can aid YOUR efforts, but there is little said about how an individual can help the team or why this is important. Admittedly it is difficult to aid someone whose objective you don't know, and with whom you cannot communicate, but there are simple things you can do that will help everyone out, not just yourself.
You mention that it's important to gather information about your surroundings and use that information to secure safe opportunities to advance you and your team. One of the most important pieces of information you're given is shown to you at the very beginning of a match-- the snapshot of the opposing team and of your own.
Just seeing the weapons that will be in play you'll know just how paranoid you need to be (Are there snipers? How far is their range? Where can I expect them to be on the map?). You also get an idea of how your role may need to change depending on the weapon your teammates have. I once played in a match as a shooter with three snipers on my team. Playing turf wars, I knew right away which areas of the map would be more difficult for my teammates to cover and planned accordingly. I also knew that I would have to be the one to put head-on pressure near the choke points to avoid the opposing team overtaking my team.
You can also use this knowledge about your teammates to help them out. Snipers usually prefer the high ground, but those without access to burst bombs may find ascending to strategic locations to be difficult. Pay attention to what your teammates are doing and try to help them out when you can. If you have access to sprinklers or a squid beacon you can plant these near a sniper's location (usually somewhere behind them) to help keep their escape route inked or make it easier for them to get back into position if splatted.
You can also think about how the abilities you've chosen can best benefit your team. If you have a swim speed up or two, you will probably reach key locations of the map before other players. Think about the weapons your teammates have and where they might be headed. Be sure to ink the paths that will benefit your team the most or that lead to key areas of the map so that your team can take advantage of them.
You mention that it's important to know when to retreat and that avoiding situations in which you die is important, but you make no mention of the super jump mechanic. Obviously players know that it exists, so no need to explain how it works, I suppose, but if you do find yourself in a situation in which you don't think you'll survive, super jumping back to spawn (or another player- you can do this at any time!) saves you time- if you died, you'd head their anyway, get a head start!
As an example, I was playing Bluefin Depot the other day and had just squidded up a wall on the left side of the map leading up into the other team's lower area. I was in a small alleyway and as I moved forward I suddenly saw paint sloshing just past the side wall. At about the same time, I hear a splat bomb land right behind me. I have a second or two before I am either sloshed to death or explode. What can I do? Thinking about it today the answer is obvious... super jump to safety. (OR, ink up the wall to avoid the explosion and try to catch the slosher off-guard as they round the corner.) [Spoiler: I froze and let myself explode. :((]
On the topic of super jumps and helping out your teammates, try to stay in a strategic/safe location so that if a teammate does super jump to you, they will be able to reach you safely- and don't leave them hanging. If you are fighting someone and a teammate super jumps to you, use that to your advantage. I've seen many players focus their attacks on the landing site; use this as a distraction to gain the advantage and take out your opponent. This keeps both you and your teammate alive. Even if you don't manage to take down your opponent before they land, allowing a teammate to safely jump to your location makes it more likely you will be able to jointly defeat any opponents (or they can at least serve as a distraction/bait) and maintain ground.
These examples are a bit context-specific, but I thought it was worth noting and I hope that it helps you to improve your guide or gives you some new ideas. I must say, after reading your guide something clicked and I realized- I know why I always lose Arowana Mall- I overextend and get killed at the choke point or in enemy territory! Since then I've realized that I'm a much more valuable asset to my team when I'm alive and keeping enemies from creeping in and holding the choke point rather than going commando and trying to rush into enemy territory only to be slaughtered almost instantly.