I will say, as someone who started out as a tank, doesn't have alot of problems tanking at 60, and has an alt that I sometimes play that is currently a Gladiator.
Tanking pre-30 really sucks, mostly when playing with people who are quite a bit beyond the dungeons level. They may be ilvl synced, but they WILL be in much better gear while the tank, at best, will be in mostly dungeon gear if that (not getting started on the first three dungeons where they most likely are still in complete whites). In general the bosses are pretty easy, but trying to keep a group on you, more so if the DPS is deciding to attack different targets, is much more difficult before getting even Sword Oath.
That said I wouldn't really say this is an enemity problem so much as a gear problem, as many new tanks are going to be at a massive disadvantage in these case. It isn't till about Halitali that it starts to get a bit better.
MRDs, atleast, have Overpower which works out better overall atleast even with the gear disparity.