They are still the really popular is both the professional (>$2000+) and the ultra cheap market segment (<$50). iPad doesn't really cater to either of those cases.
Not everyone who uses a Wacom tablet is a bedroom illustrator, even a professional bedroom illustrator. Many projects simply don't fit, and most professional applications do not have their full version available on the iPad, and that will likely continue to be the case indefinitely.
Is the pressure sensitivity equal on the apple pencil to high end Wacom?
It's really great. iPad + Apple pencil feels better for making marks, and the Cintiq Pro is just a bit behind in drawing feel but more capable overall.
iPad doesn't run professional software that tablets are mostly used with.
With Sidecar (+ a supported Mac), you can use your tablet as a second screen and apps can access the pencil.
I can't comment on the experience.
Sidecar step 1: upgrade your Mac to Catalina, lose access to all your 32-bit apps. Including that treasured copy of the last version of Adobe's apps you paid good money for before they switched to a subscription-only model.