It nerfs the damage output of burned mons.
Instead of only halving the attack stat part of the damage equation now it plainly halves the entire thing (base power, item boosts, etc)
Might aswell go back to 12.5% tick damage then. We're left with a single mechanic that has both gen 3 and gen 7 parts of it, lol.
Not to mention that when calcing we always use gen 7 because that's where all our battle mechanics come from, it makes no sense to back away from that.