Welding has always been implemented extremely awkwardly in these games because it never particularly flows well with the rest of the rooty-tooty-point-'n'-shooty that the games run off, so I won't reflexively say no to anything that shakes it up.
KF2 implemented permadeath mechanics to those doors where if a door gets broken down, it's dead for good and respawning it as a Support takes way too long that it's usually not a good idea to waste time reviving them.
I'm going to nitpick the use of "permadeath" here because you absolutely can revive them through the use of a Support specialist. Think about why that mechanic was implemented:
In KF1, you could hold a door infinitely unless it was broken down by a massively damaging attack that usually flattened it (and any player unlucky enough to be on the receiving end of the same Patriarch rocket, for example, that destroyed the door), but as long as the door didn't explode you could hold that door the entire round as long as it was constantly being welded.
It wasn't fast by any means, but it fit better with the first game's slower, more deliberate pace.
Among the many balancing decisions the dev team implemented for KF2 was limited maximum door health, i.e. doors have both a current and maximum hit point total (that is, even if you keep it at 100% current health, the door will eventually explode after it takes enough damage).
This was done as part of the balancing changes to keep players on their toes with regards to making a hold on the same spot harder, so that you can't cut off an entire avenue for the Zeds to approach by parking a Support at that door and forcing them to hold Mouse1 the entire game. We can attribute this to at least a couple of reasons:
- to avoid circumventing the devs' intended design of constantly being under threat by getting surrounded
- it makes for unfun game design having a player devote 45 minutes to an hour of their precious time on this planet to play Welding Simulator while the other players actually get to shoot Zeds
That said, the devs also knew that they'd need to rebalance welding to give players a reason to use it, hence the ability for Supports to rebuild broken doors and Demos to place explosive traps. So in KF2 you still have to commit to rebuilding and welding doors if you want to make use of them as active tools.
It's not a universally useful on-demand ability, no, but it's a situational tool that players can absolutely take advantage of when needed. The reason it takes Support so long to rebuild doors in the first place is so you don't have the stopping powers of the full weld nor the trash-killing power of door traps on command; unless you are extremely dedicated and devote entire teams to keeping the Support protected, you can basically get one per round on Hell on Earth.
To put it another way: if door traps and welding were any better than they currently are, they would absolutely kneecap the game's pacing because so much of it would be dependent on players constantly stopping to weld and trap doors.
I don't even like the traps that much in KF2 because when players randomly trap doors, it usually isn't to help me out; it forces me to check my fingernails for a few seconds while I wait for the doors to explode and pick off whatever comes through all the fog and smoke, with the Demo smiling knowing that they added a couple of crawlers to their scoreboard count.
If used badly, they're counterproductive.
KF3 seems to just do away with welding entirely, replacing the welding tool with a mine that holds the door for a certain amount of hits before detonating the door like a weaker version of Demolitionist's door traps.
Now we're getting into hypotheticals here, but: If the devs are leaning into more action-oriented mechanics, then something that's faster and less-obtrusive makes sense.
