The 200hp difference between a lvl 50 and a lvl 55 gladiator is also a factor, but long story short, a lvl 50 gladiator with a full build will still be competitive. some glads in the overall top 15 are lvl 53 or lower. Unholy Guardian and Duke Nukem come to mind.
If by competetive you mean almost good enough to win, I agree, but I dont like almost good enough so atm Im just waiting for my guys to get to lvl 55, wich will take them another couple of months. Until then the only thing ill do is to log in to keep them active. When they get to lvl 55 the plan is to buy them new gear, update strats and turn on achievments again.
I also expect my new guy currently in primus to get to lvl 55 before any of my old glads, and if hes getting to close to to BG induction Ill equip him with greys to keep him out.
Unless you plan to retire I see no reason at all to get `promoted` to Blood gods before lvl 55.