That doesn't change the fact that it's an unnecessary set of steps when having the ability to set spawns would make the process 10x smoother and easier to manage, allowing GMs to concentrate on other factors in the event and making them better. Plus just relying on people not to be dumb and actually do it within that 5 minute window is definitely a fair thing to expect, but still not certain and will lead to people being excluded just for being dumb, not paying attention or being AFK at the wrong time.
Idk what you mean by this tbh, if tacs aren't for everyone then how are they ever meant to be used to allow everyone to spawn where you want them to for the event. Plus the whole idea behind using them in that way is that GMs just spawn tacs for the people who don't have them and, yes, while people only have to set it 1 time in the event if spawns never change, people who join late still have to go through the same process that everyone went through at the start, except during the actual running of the event which usually means either the GM or a GH if there are any have to drop what they're doing just so said person can actually properly participate in the event, and this can happen multiple times per event.
Changing spawns wouldn't be permenant, at the very least it shouldn't be I don't see why if it does get coded for the server it would be considering the fact that not all maps have the same scale and having the same spawn between maps could mean actually just spawning into the void which obviously wouldn't work, so the spawns would only be set until the map changes in which case it wouldn't get in the way of any future events because future GMs will either A. change the map and spawn will reset anyway or B. if they stay on the same map just set the spawn where they want anyway