solo?

[Lissa]

They are especially gimped in being unable to wear most inferno equipment (always level 59.)

Huh? My level 60 monk's best buddy very much is a L60 enchantress. (Although the other two followers, whom I haven't been using at all, are both L59 right now.) Are you sure about this?

They have some sort of catchup mechanic in that they'll gain experience to one level below you (or just automatically be one level below you?) really quickly, even when not with you. For your current level, I think only the follower with you is gaining experience (my Templar is now 60, Enchantress has some experience towards 60, and Scoundrel has none).

This is correct, you have to take them out and get them experience after you hit 60. I did that the other two days and now all of Lissa's followers are 60. Also found that probably the scoundrel is probably the best choice for a DH as he boosts your damage, significantly I might add, and the templar is pretty crappy as a tank from what I have seen in Inferno anyway (probably since late Nightmare).