Honestly, with damage 2.0 Mk.1 does only slightly less damage than the regular braton (17 versus 20), but those damages are reparted differently (2.5/4.25/10.2 versus 6.6/6.6/6.

, making the Mk.1 specialised against infested (about 22 damage) when the regular braton is a jack-of-all-trades (about 24 damage after resistances). But the regular braton is STILL better than the Mk.1 versus infested, and by the time you even meet infested you are up to, what, earth?
It also have a ridiculously small status chance (1% versus 5%) and lower crit rate (5% versus 10%)
Mk.1 also have a slower rate of fire and higher precision. Precision doesn't matter much, but the slower RoF further decimates the Mk.1 DPS.
Holy crap, I read the wiki for this, and turns out the Mk.1 is crappier than ever. Get a regular braton, NOW.
Guaranteed DOUBLED DPS against grineer, unmodded.