How about increasing the splash radius and projectile speed? I can do more damage multiple times with a scrambler rifle charge shot, scrambler pistol headshot, and a shotgun.

The Commando buff was nice but the shield regen of 10 is still ugly to look at (just raise it to 17 HP/s).

Placon is fine, it can OHK almost anyone, but takes skill. Commando is getting a significant buff, wait to see it in action before you ask for more.

Splash damage is noob talk, see flaylock for example.

Yet I've only seen one player seriously use it against me in a skillful manner, he still went negative.

I almost always go positive with mine. I usually go about 10-2 but I get the odd 20-1 now and again.

Yeah, but that's a sidearm. When it comes to your main weapon, I think it's a little different.

I get an average of 35 kills per game on my other fits.

Then get good with the plasma cannon. It is a weapon that takes your skill and gives you results based on it. If you are as good of a player as your 35 kills per game says you are, the high skill requirement of the Placon shouldn't deter you.

What I'm trying to say is that all other light weapons are far better than the PC, even the laser rifle can be more useful than this thing. A splash radius and projectile speed increase is mandatory for this weapon.

All other light weapons, except the Swarms and Mass Driver (which I personally consider both the most easy mode weapons in the game) can't effectively destroy vehicles or installations. The Placon is the second most versatile weapon in the game, except Forge Guns, which are getting nerfed, so it might soon be the single most versatile weapon in the game.
Generally speaking, the Placon sacrifices almost all of its ease of use, to be extremely versatile. It isn't meant to be a slayer weapon, and it is working as intended.
I don't get why you say all other light weapons are better than it. Its better than an AR at blowing up turrets, and better than a swarm launcher for killing people. Its a weapon without a niche.
If you are looking to shoot and kill just people, there are many other options for doing that.
If you want to be able to shoot everything, look no further than the Placon or Forge Gun.

The direct damage for PC is so bad right now that it can'y really be used to blow up vehicles other than militia and its splash radius is terrible, so no, it's not versatile at this moment. Your comments keep suggesting that you're merely a regular player on Dust, that's concerning.

The only thing wrong with the Plasma Cannon are the glitches and bugs, as well as there not being a reason to spec up past basic.

Half the projectile speed.
Put the splash radius to 0.
Bump damage up to 20'000.
See what happens.

Honestly, there just need to be two rounds in the thing before you reload, or an assault variant like this.