Switching weapon in PlusN is possible right after making a shot from another, but then it counts some time (255ms) before making new weapon shot possible. The problem is that shooting moment can be delayed due to ping/lag delay and you will expierience weapon stuck - it looks like you tried to switch faster than server came back with "shot confirmation" and switch counter will be triggered later (not sure what time exactly, but it's like you would shot another weapon and need to wait again).

This leads to some unfair situations when smooth connection allows for multiple shots while other player need to switch slow so not to stuck with only one shot. I know better players dont need to switch so fast and focus on aiming, but when you're medium skilled and lagged then you will face 4 opponent's shots vs. 2 yours (if you wont die after his first 3).

To the point. My suggestion is making a fast switch easier, and slow it down a little to compensate spam possibility. Here's how:

Misc -> Weapon Time { Dropping = 1;
                      Raising = -100;
                      Ammo = -1;
                      Shooting = 0; }
 
Gauntlet -> Time ->         Raising = -1;
Shotgun -> Time ->          Shooting = 250;
Rocket Launcher -> Time ->  Shooting = 250;
Railgun -> Time ->          Shooting = 250;
Grenade Launcher -> Time -> Shooting = 250;
BFG -> Time ->              Shooting = 250;

In short:

• 250ms "buffer" prevents (power) weapon change but if you press a key within this time it will cause fastest possible change afterwards.(1)
• There is also a 100ms delay for all weapons (except gauntlet - it will make it more situational) to prevent too fast switch without shooting.(2)
• (1):(2) Ratio can be reversed (it would make fastest switch harder a bit), but I wanted to return to vq3 combo style: fast weapon->power weapon (the opposite is spamming friendly imo - "missed with power - spam with other").
• NOTE: It's not about these specific values (only my preference) but general switch mechanics.

Ps. Here's a testing patch to PlusN I used - might come in handy (console: /load fix)