Nothing is hard to play if you practice the instrument. There’s a difference between the feel of a Fender / Mark style amp vs a SLO/Recto style amp, but really one is just tighter and more immediate while the other has a bit more sag to it. Neither is hard to play, I’ve always found the “non-forgiving” quality of an amp to be a bit of internet fluff that doesn’t really translate to reality.
I think there's a few things that can make an amp hard to play, for basically the opposite reasons.
I used to have a Stephenson amp that was kind of like a mini Trainwreck Express, but it had an absolute ton of sag. It was great for bluesy playing, but trying to play rock riffs on it made it go "flump" instead of "chunk". Now, to be fair this was like 15-20 years ago so part of it could've been not knowing how to adjust it right or not having it paired with the right cab.
At the same time, the Stephenson had more picking responsiveness than any amp I've ever owned since. It made me really have to learn to play with more consistency to get an even sound from every note. After that it's been nice to have amps that are more forgiving in this regard.
The opposite end of the spectrum is VHT/Fryette, where the base sound can be extremely tight and "dry", so those can be more frustrating for lead playing unless you manage to reduce that with amp settings. The flipside is they are perfect for those start-stop riffs.
Finally we have high power amps that can have a lot of dynamic range especially on their clean channel where hitting harder means it's an explosion of sound. If you can't handle your picking dynamics well, this might make you all over the place.
Of course, a lot of this comes down to practice too, but I think there are qualities in amps that can make them feel harder to the player.
Marshall style amps to me are the perfect middle of the road: not too loose, not too tight, not too expressive, not too compressed.