Meh I never used repel. Once you're 16 you get a companion and at that point it's fairly easy. I personally leveled using conduit of ice on mastery(aoe slow, large aoe damage too, it tends to kill the trash mobs in one cast even though it takes a few seconds to do so), the choke for single target bigger mobs, the shield for reducing dmg and having a knockback for emergency or for finishing mobs(it does good dmg but the recast time is annoying so I didn't pop it too often) and last skill I forgot what I was using, until I got sudden storm which is like the best spell for CWs, since it's an aoe that more or less instantly kill all trash mobs. Once you have a companion anyway it becomes very easy, but even before that I didn't have much of an issue. I think I used 10potions from 1 to 35, at which point I started having to use them every now and then due to CC immune bosses and multiple pulls.
On the guardian thing, mine is amazing, but it does seem that if you don't go conqueror to have a good amount of damage, you cannot do shit as a guardian. I'm conqueror and mostly using def+power or def+crit gear and I have no trouble holding aggro on multiple mobs at all, it's actually very easy, and at the same time I often outdps the shittier DPS, I tend to be 2nd or 3rd on damage at the end. Also does pretty good solo, the aoes have long cooldowns(the aoe taunt and the shield bash line aoe thing) but they do solid damage and tend to be up every pack or so. Mostly the issue is with single target, but I pop my daily every other pull, the one that increases damage for like 8seconds, so I do fine.