Draugr can't run under water. They merely trod along very slowly. The only enemy I've seen able to climb steep inclines very quickly are wolves. And that is absolutely fine, since I know what my dog can do, and she is VERY capable and very fast in climbing at least 80 degree inclines.

Troll raids are fine. Just kite them away and deal with them mano a mano if you have at least swamp gear. Stun block them, then kill them quickly with an abyssal razor.