Well, I stuck with Faendal because I prefer having an archer for backup. Sure, I pluck a few stray arrows from my Khajiit's tail every now and then, but he's
usually a pretty good shot! Right now he has the same bow as my character, a fine Dwarven Bow (except mine has a 10-damage fire proc on it), a two-handed Dwarven Warhammer of Flames, and heavier armor than me. I'm wearing a full set of heavy Wolf armor from the Companions, he's wearing a full set of heavy Steel Plate (each of our armors have a few pieces with +health and +weaponskill enchantments: archery, block and 1-hand for me, archery and 2-hand for him).
When I hired him on, at level 5 or so, he ROCKED! He was one-shotting wolves that would jump us, and nailing bandits to the wall... but now, at level 26, even with all that nice gear a random wolf will tear him down to his knees in two bites -- and that same wolf barely touches me, even if I just stand there, and even though I have
less armor than Faendal.
So something would seem to be off -- maybe he's not really using the gear I gave him... or he's not actually getting full benefit from the gear -- perhaps the enchantments don't apply, or the stats are scaled back on an NPC... or he's levelling but not getting the same bonus to health/power/stamina that my character gets... or he's levelling at a reduced rate, perhaps being in the mid-teens while I'm in the mid-twenties... or he's just not levelling up at all with me, and is still the same level 8-10 archer I met in Riverwood twenty levels ago -- which would be
really disappointing

I'd like to know if we're supposed to be upgrading followers like we do gear, or if we're supposed to stick with one we like and level them up alongside our character. Because for now, Faendal's not good for much other than being a low-capacity pack mule. He waits nice and safe at the door while I go clear the dungeon by myself, then helps me haul the loot back to town to sell, cowering on his knees and begging for mercy every time some random woodchuck jumps out at us... sheesh!