Actions are extremely responsive to input since snapshots are instant (almost, within incompressible individual ping considerations). But I see what you mean by reactive, you want to see the damage resolve instantly.
I strongly disagree with that, for the reasons I exposed above. You remove so much counterplay with this alone that it would make the mode extremely washed out in comparison to what it is right now.
Guard is not designed to counter snapshots...
You defend against MCH LB with recuperate and mitigation. Mitigation has to be up when you expose yourself or engage, and recuperate is how you prevent oneshots. Some jobs have obviously an easier time to survive it than others, but all of them can. Spite combinations actually have a lot of variations with proportionate risk vs reward, the lowest damage ones being the most silent, and the highest damage combos being the obvious "you're gonna get nuked, better get prepared if you can, you have 3-5sec" kind of deal. It's not a question of ping (unless you have 500+, but that's a problem for every game anyway). Ping actually has other issues, even at low ping, being the position you see other players at any time versus the actual position they have server side, which is very egregious in this game.
You're right, it's not about parrying or dodging, it's about quick thinking and tactical decisions, and not just positioning. It's when to use defensives, when to keep them, when to burn them, and when to engage or not depending on their availability. Taking Spite as an example again, you have to carefully know which targets to hit with it, because while in most cases it will work at low level games (or randomly fail because people will just monkey fire it while another player will have a shield or mitigation up out of sheer unrelated luck), but it sure as heck won't work just like that at higher level.