It takes a bit of investigation and a little common sence to see who is feeding with a big bucket.
Every purebred breeder says he doesn't overfeed, what else are they going to say? So that is just a dumb question. Ask what they feed, but don't blow a gasket as soon as you hear grain mentioned. Hot alfalfa will grow out the feet on bulls too, not to mention the kidneys.
The breed average for Angus at a year is somewhere around 1100 pounds. It takes some decent nutrition to get that weight, so any bulls over 1100 at a year have been fed really well.
If you are at a sale where ultrasound data is presented, you can guess the feeding. 1/2 inch (12 mm) of backfat is a bull fat enough to slaughter. 1/4 inch is desired to get a better YG, and remember the steers would be about 30% fatter than the bull under the same conditions.
Next is how some are selecting the epd for fat thickness, thinking it leads to easier doing cows. This is not a direct corolation! Fat thickness epds are adjusted to 1 year of age and have nothing to do with a cow's doing ability at maturity. I have daughters of bulls that have moderate gain epds and positive fat thickness epds, they are the hardest doing group of cows I own.
Going back to the way the bulls are fed, show up at feeding time. If the breeder won't tell you exactly what the bulls get, why not? Maybe he fears a bad reaction, but if he knows his ration is not too hot he shouldn't mind at all.
Bulls fed just hay will likely be sorry looking at 1 year compared to grain fed bulls, buyers need to be willing to pay for what they say they want to get sellers to reduce the feed. If you see bulls in that 1100 pound range with "no grain" investigate how that is possible. Maybe bull ration isn't called grain in some places, silage made from grain crops can be high energy, too much protien being fed compensates for lower energy.