Um no, I don't think the pc was the problem with Heroes 5. Its been a while since I played it, but even with my current pc it still ran slower then expected. The game wasn't well optimized. Heroes 6 on the other hand, yeah very well optimized. I don't think Tribes of the East has many more artifacts or maps on offer, but the extra choice of upgrade in units really makes the game interesting as you need to get the units based on the type of strategy you choose to follow.
For example, the Dungeon scout unit can also be upgraded to a "stalker" < think that is the name, which instead of shooting goes invisible and comes right up to the enemy unit to attack. So if you are doing non siege battles then they seriously become a unit to consider offering that well needed depth that you are seeking.