The support, I always thought, is the most misnamed perk of the bunch. He's certainly NOT a supportive perk. The only thing that truly goes into that role is his capacity to give out one free mag per wave (which is already a great way to make the perk useful !)
No, in my opinion, the support is the perfect balance between a nuker like the Sharp' or Demo and a crowd control perk like the SWAT, Firebug or Commando. Of course, it depends on your weapon of choice (the boomstick is better against mid-to-big zeds while the M4 is better at dispatching multiple smaller ones). But all in all, the support can deal with pretty much anything with little to no hassle. He's also fairly simple to play with... and be effective with. You pretty have to aim and fire ! Every game need a class/perk/character that is not overly complicated. Plus, while not as tanky as the zerk, as he's always up-close and personal, he's also one that often soaks up a lot of damage, which can also help him be an useful part of the team.
As for welding doors... Yeaaaah, I barely see that, if at all. It doesn't help that doors are permanently broken if zeds breach them. Also, camping is not as useful as it used to be in KF1, since the husk can kamikaze and spray fire for example. Zeds are more nimble too in general. So it's really more of a gimmick or a relic of the past.