I don't think you even know what a "chain gun" is. Where did you get this information from, reddit and video games?

Chainguns are a type of autocannon. Heavy, light and general purpose machine guns, like the M2 Browning, M249 SAW, Maxim, Been Gun, MG3, etc... none of these are chain guns. They aren't even all belt fed, which I guess is what you meant to say because I think that's the videogame midwit lingo. They are nonetheless universally accepted as being very valuable in combat.

Most gun designs that included N-round burst have eventually abandoned it because full auto with operator in control of burst length turns out to be superior, while at the same time the mechanism needed to force the burst is an extra point of failure and negatively affects trigger pull .

Most recently, it was Russia dropping 2-round burst on AK-12 after experience with it in Ukraine. M4 is another famous historical example.