I had that same question back when I got into RC cars after seeing the Legends classes run at two different tracks in the area.
When I asked the hobby shops at both places I got the same answer. Neither of them ran the Legends rules. They said the rules for the power trains were too hard to deal with and didn't allow for using the stuff their drivers used in other classes. What I found was all the Legends class drivers had batteries from their other car classes. Nobody was running any one cell batteries. The majority were running 17.5 motors. With ESCs to match. There were some 13.5s and such. I've yet to see any car that had the Legend's rule motors or batteries.
Both places had healthy Legends races. The turnouts were almost always bigger than the 17.5 breakout truck classes which almost always had the 2nd largest starting grids. The Legends almost always had multiple qualifying mains. I say "had" because one of the tracks recently lost their lease. It had decent turnouts, it just so happened the property owner got an excellent offer for the property.
Both places had the largest turnouts in the breakout classes because they ran them with tech inspections. Other than Minimum clearance that is. Oh yeah, and the Legends had to have an original chassis. That was it. The breakout time does enough "tech inspection" according to those track owners.
I've got a 2S 4000 brick in my Legend. Same in my breakout truck.
Look around the pit tables and ask the guys at your track what they're running. There's always someone around who'll be glad to talk.