Forts IRL carried some real use in that you'd stall for reinforcements...not bad especially in times before professional armies existed and people were relying on levies.
Also before modern time coastal forts were nigh-unassailable by ships. This was particularly relevant to the Bosphorus strait because it's so narrow, but it was not trivial elsewhere either.
Claiming they were "not useful" is definitely inaccurate. They won't win you offensive wars by themselves in either game or IRL, but they can be significant to the outcome.
Forts are/were pretty useful as a base for roving patrols too.