For mass use, sure, but special ammo is already situationally quite useful.
Burning folk never gets old. It's OK to do less damage (especially on DOMINATING, fighting bosses which you aren't likely to one-shot/one-burst anyway) when the result is likely to be a panicked enemy - a 9-round long burst is about 98% likely to set the target on fire, and I like those odds. The micro-shrapnel ammo makes for a great crit opener, putting a big debuff on an enemy - Ancient Rathounds are a favorite of mine for that since they're so very resistant to other useful CC abilities. And contaminated ammo is nice for the stacking +damage debuff, especially on more resistant enemies; I like tagging Balor with a round while he's stuck in a trap or stunned, then going to town with the W2C.
Sure, for general use, the general use ammo is absolutely better. But I think there are enough special cases that special ammo is still worth crafting and carrying a couple magazines' worth.
Incendiary ammo works if you're burst firing, for anything else the odds of setting a target, let alone a specific target, on fire are very unreliable.
Micro-shrapnel would be great for every weapon type if it was 50% extra damage 100% of the time, though it's fairly okay as it is, too. It's biggest problem is that it doesn't do much against targets with very high mechanical DR/DT. What do you mean by debuff, though? It's just extra damage over 3 turns, it doesn't debuff or control the target in any way.
I fully agree, contaminated ammo is good.
Explosive ammo is... okay, I guess? The Tommy Gun can certainly be hilarious if you hit something with an explosive burst.
Shock and acid rounds are kinda meh. Unconditional extra damage is never bad, but the numbers are not exactly mind-blowing, either. They would probably be awesome if the damage benefited at least a little from the skill multiplier, though.