Ah, that makes me feel better... its more grinding than skills required (I can do the grinding)
You say that, but tbh if uve played enough to be para 400 you should be way about 35 and already pushing into the GR50+ atleast I think I was farming T10 before I was para 200 this season. Perhaps link your armory so we can see what sort of gear you have as it seems your a bit behind the curve on what ure clearing compared to your level.
As an answer to the original question, the easiest class to do a GR60 with would be a crusader because once u have full invoker your practically invincible at that difficulty and you just run through, clump mobs and hold down LMB on the champion. It's also the least paragon-dependent build early on as it gains nothing from CC/CHD meaning that a para 800 isn't much stronger than a para 400 for that build.