Gaël has a LOT of potentiel and progress margin for sure.
But they shouldn't be compared like that since they all have some very serious wicknesses and very very different strong points going for them.
Gaël isn't agressive enough overall, which is a shame when one has a FH and a fighting spirit like him. And on some occasions he takes unconsiderate risks hitting brainlessly, and on some others holding his shots back. His volley and movement isn't academical at all but it can be very efficient.
On his part, Paulo thinks too much and as you said is
at times. Like Gaël, he "can't" play on grass.
Richard has a lot of problems dealing with pressure and winning big matches. But saying that he would lack heart is IMHO very unfair and even false. And he can play on all surfaces and technically (in terms of tennis shots) he's the most complete player but being a complete player isn't everything.