The learning curve is actually really flat, more like windsurfing
Takes years to master things well, for most riders I think.
Can not see any advantages being used to directionals though - when learning.
Of course, the initial task of getting "up" and being able to foil for a longer distance and faster - this is a really steep learning curve yes agree
But from being a beginner (able to ride for longer distances), to being good, it takes a lot of hours and time, just like windsurfing IMO, where it takes many years to get "good".
It is fine though, that the initial "getting up and ride" is okay fast, so you get totally hooked really fast, and feel like you can ride forever and a great feeling !
But, especially if used to directionals (as they turn in a completely different way) I think, the next learning curve takes a huge amount of time (at least for me, and many others).
The next stages is being able to turn, make turns on a wave, ride confident toeside, jibe, foiling jibe, tacks, 360s (and if strapped, jumping and spins/board offs etc)
This is the stage that takes time, unless you are extremely skilled and fast learning (the best are + they use a LOT of time on the water)
I love this gradually learning curve - because every single hour you put into it, will make you better - and you can slowly but clearly feel and see this over a long time - AWESOME
At least my view on things from personal experience, and when I talk to fellow hydrofoilers.