why does a three year old need to beat older? well, a race such as the derby is restricted...so when meeting older horses, that's an open field, anyone can enter. kind of like a horse who beats all comers in a stakes would be considered better than a horse who only races in a restricted race, such as ny-breds only facing fellow ny-breds....
and yes, a filly would be given more props for beating colts, rather than just other fillies.

open comp is one key.
setting/tying records is another. ruffian for example..beat all comers, as well as the clock, and never headed. that's greatness.
round table, excelled on turf and dirt, 17 tied or new records, the most ever. great horse!

personal ensign, undefeated. beat colts and fillies. she was great.
azeri, a nice win streak, but didn't win in open competition...very good, but not great.

of course back in 'the day' a win while carrying far more weight was something, as was a narrow loss while giving a lot of weight....that doesn't happen much these days...however, congaree got a lot more praise in his very narrow nose loss to milwaukee brew than MB did for winning! congaree was giving weight...
also, dr fager set the mile record while carrying 137 pounds(if memory serves...) that's GREAT. najran tying the record years later....mmm, not so great.


horses have dazzled with great performances...GZ in the bcc, candy rides win over MDO...but a great performance doesn't make a great horse. they need to back it up.

smarty could have been great...so could alex.

to really know tho, if a horse was great. come back in 20 years and see how many of todays horses still get press. those are the great ones.