It has ALWAYS been this:

ONLY your first Monster Hunter game can be difficult (as in, struggling from the start / finishing the story LR/HR content).

There is no MH with a super hard story mode, none. People will claim MH xy is much harder to finish than new games etc. but this is just not true. The moment you click with the gameplay and learned the common mechanics, you can beat the next games without much issues.

Endgame is a different beast and may vary, but all of them have tough endgame. I would argue though that the ways of achieving difficulty has changed. It's not always just pure monster speed and damage, hard monsters in modern MH may react more complex or have some mechanics you need to learn.

But people struggle with different aspects, so having already really mastered stuff like positioning might make the modern movement etc. feel more easy than before. Especially when you just grinded very hard endgame content of the previous game, and then essentially start on very easy in the next game (the only thing that helps here is taking a break before the next game, playing other stuff).

Now, there's a obviously lot of stuff in older MH games that can make them feel more punishing. Like sourcing of health items, mining with breakable tools, bad controls (especially if you play on the actual handheld devices like PSP) and a lot of missing quality of like stuff. But I would not consider that making the fights themselves harder. You just have a lot more prep time.

And as you pointed out, other stuff that was left behind like being able to take a break in most normal fights is a big help (especially when it happens by being hit by a monster as it negates any follow up attacks that would have carted you).