I think Beasley has a lot more untapped upside to him than he's shown over his first few seasons, but overall I agree with you. Too much ego, and 3 guys can't win. Their bench is devoid of serious players, and (just speculating here) their cap space has got to be at a pretty negligible figure after these 3 monstrous contracts come into play, leaving them very few options to pick up any "real" bench help.
Look at their current roster, minus "The New Big 3:"
-Michael Beasley
-Da'Sean Butler
-Mario Chalmers
-Yakhouba Diawara
-Kenny Hasbrouck
-Udonis Haslem
-Jamaal Magloire
-Dexter Pittman
-Quentin Richardson
-Jarvis Varnado
-Shavlik Randolph
Yeah, that has championship written all over it...
And even if they are "the team to beat in the Eastern Conference," that's not really saying much at all. Being the team to beat in the East is like being the lead usher at your local movie theater. Yeah, you're the boss of the rest of the ushers, but its simply not that big of a deal. There are more complete and better teams in the West, and the balance of power has been in the West for a pretty long period of time now, this, IMO, doesn't really change things all that much. (No offense to movie theater ushers.)