The ability of the drill to not load down has little to do with efficient hammer drilling.
The problem is if the hammer function is not powerful enough, it doesn't cut the concrete but burns and blunts the bit. Sounds like what you experienced.
I did a job in a high school football stadium where we had to refasten the loose bleacher uprights to the reinforced precast concrete tiers.
Hundreds of 1/4 x 3" wedge anchors.
For a job like that you need a dedicated industrial grade hammer drill like the Hilti I mentioned, got probably 200 holes out of one bit, but more importantly, your arm didn't feel like it was falling off after a day of drilling holes in concrete. No struggling with it, little effort and very comfortable to use.
I can't comment on the other brands but I know the Milwaukee would of failed miserably put to a task like that. and Milwaukee use to be the contractor standard.
JB.