I really don't understand your logic of increasing the zeds instead of buffing SWAT.
It's a trash killer that isn't completely justified by the current game's trash setup. It has a better place in Controlled Difficulty where the zeds are more numerous and it has more fast-moving trash to kill. Ergo, increasing the max monsters would give it more trash to kill and justify picking it by proxy.
Again: In the context of having a number of specialized roles that need to work together, SWAT is fine. It just hasn't been hit by the power creep that the rest of the game has, most of which is in the form of stupid weapons (like the FAL for Commando). So neuter those to bring the other perks back in line with SWAT.
most of the things it has as "skills" other perks have as PASSIVE skills.
Elaborate? I don't know another ballistic perk that has SWAT's particular skill tree *as passives.* Nor, in fact, has its passives as passives. Commando has Fallback, Elite Reloads, and Impact Rounds as skill trees, but they aren't passive; they're conscious decisions to pick one skill over another for certain loadouts.
I admit it could probably have some changes to the skills that basically give you armor and an extra pistol to start out before you switch off. I'm assuming these exist because TWI had a very specific vision for this perk in mind (which is basically the RRLRR tree), and then they realized that they needed some other skills just to have the illusion of choice. But the perk's performance in endgame is fine. It takes extra shots to down Scrakes and has trouble with FPs, which isn't bad--it's not designed to be strong against HVTs, but with Cripple and flashbangs, it helps. I can live with it having basically one good skill tree.
I admit that SWAT is one of my current favorite perks, both in how it handles and how it hasn't snuck in too many OP things. I love playing it. It's just that most of the time, a team won't have a Commando, and that gets picked first due to being able to extend Zed-Time.
The only actual buff that would make sense for SWAT (read: not giving it stuff like Stalker-vision, or more stupid crossperk weapons that don't belong on an SMG class) is a damage boost or ammo cost reduction. The damage boost is trickier because you risk messing up breakpoints and making it too good at killing med/larges for a trash class. The ammo cost reduction, while nice to have, really doesn't benefit players who are already good at SWAT.
I don't like the idea of giving yet another class weapons like riot shields and stuff because it has the knock-on effect of basically encouraging players to accept that they're supposed to tank hits, which is counterintuitive to playing SWAT well. There's a reason for Berserker to have *some* tankiness being a melee class, but SWAT is meant to cut down Zeds before they reach the player(s).
So. Having said the above: what do you want to see for SWAT?