It isn't that hard to do if you prepare properly, and the window where you even have to worry about 'holding' aggro is pretty short - once everyone else goes to fight Suulomades, you could spend half ytour time blocking if you wanted and you'd have no chance of losing aggro by the time they get back.
Further, most people are smart enough to save smites/haste boosts/etc until Suulomades and don't burn them on the innitial horoth whacking, so its easier to hold aggro there than it would seem.
If you're really stressed about it, you can always grab initial aggro in a DPS mode, then swap away when the party leaves. When we do hard or elite speed runs, I tank with my epic sos+righteousness when I have all the healers available, then swap to shield when everyone else is on Suulo so I can be healed by a single person easily.
Aggro issues are bigger if you tank vod regularly, since he resets aggro so frequently. Vod is way easier, thoguh, with a lower ac threshold, so its easier to make other gear swaps that increase your dps and consequently your threat, like power attack, twfing, etc.
When you're packing +235% threat and 16% doublestrike with a silver chaosblade, its actually not nearly as hard to hold aggro as it might initially seem