So I'd heard great things about what a cool follower he is, etc etc. So I did the mage college quest and his personal quest (90% fire resist makes his scrolls actually useful), took him on as a follower, and loaded him down with destruction staffs, mage-friendly enchanted ebony armor, health-drain legendary ebony sword, +30 stealth boots, etc etc.

So what's he doing for me? Hanging back as far as he can and dual casting sparks EVERY FREAKING TIME. Thanks for the what, 24 damage per second? To bad it takes me like 5 seconds to finish most combats, and my enemies all have 200+ health.

So far he's been handy for spotting enemies I didn't see - the sparks are like a big laser pointer that at least goes to the enemies general location (because it also seems his aim isn't that great). Other than that though, he's just a big chatty hairball. When I fought my last elder dragon, he didn't even bother showing up until I;d killed the thing. My fault for running, I guess.

I never had this issue with Erandur - he made vigorous use of every staff I gave him, often dual wielding them! I figured a destruction mage would do the same, only better because they'd use less charge.

You may need to use one of the tricks to get his stats to update to your level because otherwise, if he spawned at low level, his actual combat stats will stay low regardless of his current level.

Also bear in mind that many armor enchants don't help followers (and that includes most skill boosting ones).

All followers are locked to the level you are when you meet them the first time. There are console commands to change that, but as standard thats the way it is.

Not really. Use Wabbajack on your companion to transform them into something else and when they turn back, they'll respawn at your current level

I think the followers only use what they are the best at.

Just a guess, but I think if you give a follower heavy armor when they are always wearing light armor they wont use the heavy, but will switch to the better light armor. If you give them a one handed weapon when they are best at a two, you have to take the two handed from them before they'll use it... But if they use a two handed and give them a better version of what they have, they'll equip the better... More info on this would be cool

So perhaps J'zhargo is best using his own spells rather than any of the staff's you gave him...

I never liked J'zhargo as a follower. Illia seems to be the best imo.

I dunno about that. My other followers (Lydia, Erandur, Jenassa, Uthgerd) seemed to use whatever they had that would cause the most damage (highest base damage rating) - I had to take two handed weapons from them to get them to use shields, even if the wiki said they were trained in one handed but not two.
I suppose I could try getting my stuff back from Erandur, and see if J'zhargo would use that, but it seems unfair to take stuff back after I cut him loose... plus its a pain in the ass dismissing one guy, taking on another, grabbing all his stuff, then going and finding the first guy again. By all reasonable standards, the stuff I gave J'zhargo is better anyhow.
Maybe he's holding back on the dual fireball staffs for fear of hurting me... but that's why I'm wearing 90% fire resist gear! I wanted to bring the bomb, and instead I got... sparks.

Silver lining - I can stand there practicing my "Block" skill while J'zhargo whittles the enemy down with sparks (and then moves in and uses his claws when out of Magicka, despite having a legendary, enchanted ebony sword and legendary ebony dagger). Its gone up by 5 points since I took him on. Other followers did their job a bit to well for that to work.

Yeah my input was only from the brief times I had followers with me and trying to get them to use the gear I wanted them to use, using them to lvl up a character in that way is a pretty cool idea... they always just got in my way and force me to step back lest I either killed them or they started combat with me lol