Or you could just make it balanced with careful implementation.
A. Low accuracy while firing on the move so you can’t do drive by attacks.
B. Slow disembarkation speed so you can’t just dump troops out up close instantly.
C. Low rear armor so it’s risky to do close in attacks.
D. Instantly kill the embarked unit if it dies so it’s very powerful, but very risky if you lose it.
E. Relatively high cost so you don’t want to risk losing it by diving.
If you are going to make it clumsy, awkward or expensive then, frankly, what's the point? Flavor? We could put something actually useful and possible to balance in its place. Okw has too many high impact infantry squads to add increased mobility to the faction.