The M4 was inferior to the Tiger and Panther in some ways in general it was probably supperior although not by much to the MK-IV. In Normandy and indeed across France the Germans had the advantage of being on the defencive as well. In any case M-4's caught fire when penetrated at about the same rate the German tanks did (indeed less than some while a bit more than others although it's not clear that any of the differences are statistically significant). It's not at all clear that those are the two most important aspects by any means. If you are talking a 1 on 1 tank duel then you can make a pretty good case for it. If you are talking an armored division vs another armored division then it's simply not the case. Is there? Certainly not from what I've read. Not really. Or not. A fact that is worth remembering in this regards is that more tank crewmen became casualties outside their tanks than inside. Artillery and small arms killed more tankers than AT guns did (whether vehicle mounted or not). That would explain why they ended up scattered across that same countryside in allied hands now wouldn't it.