First of all, I wouldn't be so sure that the Swamp has low speed. They aren't slower than Rampart or Necropolis – two units that can reach the enemy from the very first turn, and that's a strength.
The lack of HP is easily compensated by excellent defense. Unfortunately, I don't know the formula for calculating it, but based on my experience, I can say that an extra +10 to the defense stat is a worthy compensation for the missing HP.
In my opinion, you shouldn't play defensively with the Swamp; you need to attack, and with everyone, because there isn't a single truly slow unit. And even better, the hero should have an Air or Water expert skill – for mass fast or mass prayer.
Secondly, a huge plus is the location – usually in the swamp. This greatly simplifies the task of defending the castles. A normal enemy will be the last to venture into the swamp, because if they enter without pathfinding and logistics, it will take weeks, or even months (!!!).
Are you kidding? You compared it to Rampart. Rampart has Pegasi, for example. And what about Dragons? Dragons are much faster than Hydras. And Centaurs? Rampart is in the top three fastest. And in defense, the Swamp's troops can sit and hold their ground; they have such high armor that they can stay in the castle walls for a very long time. The walls are more likely to collapse faster than any part of the army will die. They are more resilient due to their armor, although their defense won't save them from magic. They are more vulnerable to magic, because magic completely ignores armor, and the Swamp has relatively little health. Well, an Air or Earth expert skill would be good for everyone.
I completely agree with the rest.
