You're gonna have a tough time arguing that the dear old Mossie would have made a better point-defence interceptor guys - one of the Lightning's specifications was it had to reach 20,000 in under 6 minutes. In terms of speed, the fastest Mosquito did 437mph - so a fair 5mph behind the P-38 - but all Mossie marks hovered around, and mostly above, the 400mph mark like the P-38. In terms of gun concentration, there is no way you can argue that the difference between a Lighning and a Mosquito in this respect would have any effect whatsoever. There was not a single operational aircraft in either theatre that was small, and tough, enough to be more susceptible to the Lightning because its guns were 3-4 inches closer together - there is no realistic situation I can think of in which all of a Lighning's guns would hit and a Mosquito's would not. In this area the two planes are as good as equal.
In my opinion, if you had to use either the P-38 or the dH 98 as a BoB style daylight interceptor, which is an absurd suggestion anyway, the P-38 would come out top. At night the Mosquito would get my vote every time (despite some useful nightfighter Lightnings appearing towards the end of the war) - it's record is unequalled. As a bomber you cannot seriously make the argument for the P-38 being better any more than you can argue that a Mossie was the better interceptor - the Mossie could carry an 8,000 lb bomb if it had to, and put it right on the target. The Mosquito was renowned for being able to bomb from 30,000 ft to within 75 yards' accuracy using Oboe equipment.