Especially in recruit gear, don't expect to hang with marauders or snipers attacking you who have full BM and WH gear. I know people will come in here and say that gear doesn't matter, only skill, but that will only get you so far. So, in other words, YES, you do have to grind and take your beatings in warzones by people with better gear than you so you can stack up coms.
As the others have mentioned above though, you aren't meant to output a lot of DPS if you're a tank. You're meant to ruin the other team's day. Tank spec guardians are extremely useful in huttball. Instantly casting stasis without having to channel it, force push, Awe, hilt strike, guardian leap, all of these are extremely useful in situations like this. Also, be sure to always have a guard on someone (doesnt even have to be a healer. When I was tank spec, usually I'd just guard whoever looked like they knew what they were doing. I got huge protection numbers by doing this) Also, make sure to cast your AOE taunt as often as possible, especially when everyone is bunched up on a door in voidstar for example.
If you want pure damage output, I would recommend speccing for that. After I got bored with tanking in warzones I switched to focus spec and haven't looked back since. I now put out about 200K damage on average, sometimes a lot more, sometimes a lot less. Just depends.