Swamps are indeed a terrible place to go for a jog. Especially in heavy armor. But this opens new tactical options and considerations for the shrewd commander.
The disadvantages will also hamper the enemy, so meeting him on equal yet difficult ground is viable if maneuvering proves too costly in terms of time or fatigue. Force the enemy to make a costly approach by at least perceivably outmatching their ranged capabilities and receive the staggered and heaving charge with a readied battle line.
In my neck of the woods, there was a historic battle between an opressive count and his subjects where pretty much the above happened, leading to a proverb indicating that cunning outclasses strength or some such. There’s even a folk song. So fighting in swamps is obviously glorious ;)
On the wonky starting positions in terms of the terrain not conforming to the battle line, it does tend to make for a more differenciated play when starting pitched battles. Unless you mean starting in a pit and being unable to climb out. That shouldn’t be a thing.
