Well yes and no. In a way the features such as immutability and algebraic data types are things you should know about as a software developer even if your current language means you can't use them at the moment.
My 16 year old son has learned Rust coming from a python at school background and is now writing small games in the bevy game engine.
Having to understand monad transformers or another kind of effect system to get anything working is a heavy load that's unnecessary in other languages.
I'd say knowing how to use monad transformers is the barrier between intermediate and expert Haskell programmers.
How do you think the folks on Java and C# find their work worth doing on their end in that case?
runState do
value <- get
put counter+1
You set up your pipeline in terms of monads and then when you want to execute it you run it in IO. You can generalize IO to MonadIO or define an alias to some transformer pinned at IO. It adds a Computational overhead. Transformers are a solution to monad composition which isn’t naturally possible.
Effect systems and monad transformers are advanced topics. They're possible to use in my language yet most people do not and can still write software.
Certainly no need for them in Haskell to be successful. You can just program at the lower levels of abstraction common in other languages.
The only difference is that Haskell's community tends to emphasize abstraction
"The common expression "a steep learning curve" is a misnomer suggesting that an activity is difficult to learn and that expending much effort does not increase proficiency by much, although a learning curve with a steep start actually represents rapid progress."
https://en.wikipedia.org/wiki/Learning_curve
When writing, consider "challenging learning curve" instead (I'd love other suggestions too).