And who says I use that mod at all? This thread isn't about the balance in the pack it's the balance of the mod itself.
Acutally a vorpal enchant from red power makes it not very painful at all to collect three. Me pointing out the wither farm is more about how easy it is to engineer the fight to be crazy easy. The only issue at that point is finding the skeletons, which it can at times be a little annoying, but a typical standard mob-farm can actually make that just as easy.
Also, soul shards will be changing how it does wither skeletons, if it hasn't already. Same with angry and villager zombies. Also, arguing the balance of a mod by itself here is a bit, well, awkward. If you only had portal gun installed, it would be incredibly hard to get. A beacon might be easier to make. However, in the mindcrack pack, it's probably no harder than keeping a batch of industrial grinders going, or in the dw20 pack its probably doable after you get your base situated.
I've always found it's hard to judge how powerful travel mods are. By themselves, something like mystcraft or portalgun are almost worthless, but get more and more useful when you need that travel for large tech projects. The portal gun developer seems to either expect you to use mods that make killing something like the wither much easier than vanilla, or expects you to dungeon crawl/explore enough to find them. Seems like he is at least getting close to what he considers a balanced recipe. Balanced in his eyes, of course, balance is in the eyes of config writers and coders.