I believe a P38 has a smaller profile then a P51. But it's no way easy-mode. If anything, it's the hardest plane to master in the planeset.....IMO.
The 38 is not great in anyone area, but not bad either. The true 38 sticks have been around for awhile and know how and when to exploit the other planes weaknesses while playing to the P38s strong points at the right moment in a dog-fight.