Did the creatures/Monsters/Demons/Angels get depowered in later seasons?

Sam and Dean have become stronger hunters, is all I can say. Over time they have become much more skilful and knowledgeable in how to kill the monster that this over powers that original threat. They have so much more resources than they have ever had before. They are much more stronger than they ever have been. They work exceptionally well together as a team. The Bunker has also allowed them to grow, knowing how to kill the monster much quicker, because of their speed in finding ways to kill the monster.

I'm rewatching it right now (watched the first seasons a while ago) and... yes and no.

Monsters, angels and demons have become a joke, that's true. But I don't think they have been depowered. It's more about they way they're written.

Imagine you're a demon. You're immune to everything EXCEPT some specific blades. And you have Telekinetic powers. What do you do?
- You use your Telekinetic power to make some useless throw and the beginning and you don't use them again, why would you, huh?
- You never use your Telekinetic power to catch those blades. Why would you do that?
- Since the only thing that can kill you is a blade, which is a melee weapon, you get into a fight with your bare hands, because that looks like a great idea. Bringing a gun? why would you? And of course you pay zero attention to those blades which are the only thing that can kill you. It's rolling in the floor? Let it roll, what could possibly happen? Somebody is holding it? You turn your back on him, what could go wrong?

This is just part of a bigger issue in the series: there's a pile of non-sense and deux ex machina. There's no internal logic. At the beginning, Angels were written as some alien psychology. Later on, they look like a rip-off of Vampire RPG clans. You have Malachi (Brujah) vs Bartholomew (Ventrue)... seriously?? There's lot of copy and paste and just because. Not to talk about the post-Bobby safe house which is a clone of The Librarian one.

Still... it's kinda fun. And it has very good episodes once in a while. The average quality in the Urban Fantasy genre ranges from low to... rock bottom, both in series and novels. Only thing in this genre that made me say "wow, that was good" were the three first volumes in Anita Blake (the rest is garbage), and that's not exactly a ton of content. There's a lot of non-sense in this show, yeah, but it's still better than most in the genre.

Everything got "depowered" in the later seasons, the use of villains, locations, threats, etc.

I agree angels definitely were. In the first angel appearance, Castiel walks through every known ward and ignores every weapon Dean and Bobby can use against him and he does it as if they were throwing glitter at him. As time went on more and more symbols could ward against angels (even though on that first appearance the hunters admit they can't find anything to use as a ward, they were just throwing everything at them), humans could sometimes go toe to toe with them.

I can understand why they did it. Creatures that powerful don't make interesting characters and Castiel, especially, would have been a problem interacting when he should have been able to destroy anything that came against him. But I was still a bit disappointed.