In past titles, was it possible to fight the harder monsters first and then the low-tier ones? Or is it going to be possible in this one? That could be interesting. Although I don't know if I'm missing the point in something that makes crucial to fight monsters in a more sequential order. The basic premise is very tempting, though. Sounds like an ideal time-sinker.
I would say you are missing the point a bit if that's how you want to actively approach the game at all times, but there's definitely room for experimentation in Monster Hunter. Monster Hunter isn't an RPG per say, but the stats of your weapons and armor are still pretty important in making sure that your damage output and defense scales better with the increasingly challenging monsters. That's how the time sink works, you get to a new area, craft new armor and weapons, and now you can kill the harder monsters and move to the next area. Though it's important to note that most weapons and armor sets scale pretty well for a lot of the challenges in the area/beginning of the next area you got that armor set from, so it's not like you need to grind every monster, moreso the ones you choose and only when you hit a new wall.
Monster Hunter's difficulty isn't really a traditional "this is the super hard monster, and this is the easy monster, so I might as well skip the easy one". At least, not for the pre-World ones. Most monsters, even the early game ones, have some kind of check to make sure the player understands some game mechanic or know how to counter something. And of course depending on what weapon and armor set you have, some monsters might be significantly easier for you than it is for other people, and vice versa. That's why a lot of people have different "walls" in which they have to train to fight one specific monster, because everyone kind of has different experiences in what mechanics they have to learn or what builds and weapons they have to master.
Though as previously mentioned by Shaunodon, you can go on expeditions, which are like a free roam you can do in the areas you've unlocked. However, and I may be wrong on this but, I don't think EVERY monster in that area is available as soon as you go on an expedition. Some are unlocked when you first encounter them in a story moment, for example. I might be confusing that with the mechanic though where challenging monsters you see in other stages eventually come over to previous stages you've been in.
I wonder ... since we already got Mizutsune (one of the flagship monsters of MH Ultimate) back. Might we get the other three back as well ? I remember Astalos and Glavenus being some of the hardest Monsters to beat with my short history with this franchise.
Glavenus feels like he should be a shoe-in considering he was in World's Iceborne expansion and from what I understand the monsters which were already in World are using the same textures and models in Rise (I.E. Rathalos and Rathian are using World's models).
But if they don't get in, remember we always have free updates. I think World got ... 6 new monsters through free updates?