Hello I am here with a little thing that annoys me once again.
Something that's always annoyed me is when gyms have a huge or noticeable level spike from all the trainers around the area, or have levels that don't really make much sense for the point in the game that you are at. Shoutouts to Brock, Roxanne, Misty, ect.
Usually this isn't an insurmountable obstacle casually because in most cases you can get a pokemon that is able to solo the gym leader, or dent it enough for the rest of your team to pick off, although it can still be frustrating or annoying. It's a way bigger problem if you're doing some kind of challenge run / self restriction though, cause it means that you have to train a lot more to make sure that you're closer to par with the gym leader.
This could easily be solved by introducing higher level wild pokemon to fight, or at least offering more trainers to fight early game before you get access to some kind of way to re-challenge trainers. (Also why the hell did they remove the vs seeker that was so useful for grinding and it was a fun feature.)
Also shoutouts to rom hacks that constantly dump levels on trainers and gym leaders and force you to constantly level up so you can't actually enjoy the game.
I'm going to have to agree on the Vs. Seeker. That was such a useful item. My only guess on why they removed it is that it could allow you to get too much money? For example, In FireRed and LeafGreen there are two Ladies in Resort Gorgeous that can be rematched for an insane amount of cash. 9,800 and 10,000. It's double if you use the Amulet Coin. That's not two bad because that's in postgame, but perhaps a more extreme example is in the Sinnoh games, there are 4 trainers near the Pokémon Mansion that you can rematch for near infinite cash. I guess they decided that players couldn't put in the time and effort to grind up cash. That's the only real logical reason that I could see that they would remove it for. It's definitely much easier to train up against trainers than wild Pokémon.
The later games did at least have try to have some decent grinding spots. Gen 5 had the Domes, but while those were nice, they were definitely a step down from the Vs. Seeker. They also had Audino, which was really nice for grinding because they gave a lot of EXP, but it's kind of slow and tedious. Kalos has the restaurants, which funnily enough would give you Big Mushrooms that you could sell for big cash. ORAS had the Blissey bases, but that was something the community created in a way, not necessarily GameFreak. Gen 7 imo seemed to tone down the Exp. Share by a fair bit. It's can still be OP, but it didn't feel as bad as gen 6 to me. I can't think of any places like the Domes or the resaurants. LGPE are pretty different from the other main series games I their mechanics, so I can't really comment on that. No comment on Sword and Shield, I haven't played them. I feel like the Vs. Seeker would have been really nice in gen 5 at least. Now that I'm thinking of it, the later games did at least make an attempt at making good places to grind EXP.
One really terrible example of a bad level curve imo is the Elite Four, especially in Diamond and Pearl. Volkner's ace is level 49, and while you do go through both Route 223 and Victory Road, because this was pre gen 5 Elite Four, the Elite Four get higher leveled the further you go through them. The first Elite Four, Aaron has level 53-57 Pokemon. Every Elite Four after him have all of there Pokemon 2-3 levels higher than the previous. Cynthia's Garchomp is LEVEL 66. LEVEL 66. That's absurd. It's so bad, that Platinum dropped all of the them by 3-4 levels. Ridiculous. Honestly, the Elite Four in the first four gens have some pretty bad level curves. It wouldn't be too bad if they gave really great grinding spots that let you catch up easily, but they normally don't. In most of the in game tier lists on this site, you'll see that most of the people who post there end up being pretty significantly underleved when they reach the Pokémon League. To be fair, that's usually with minimal to no grinding. I guess in most of the games you can use the mascot legend, but even they tend to be underleveled.
Roms tend to have problems with level curves. Roms like Dark Rising are infamous for the horrible level curve (to be fair that one is also infamous for other reasons). Another example is the rom I'm currently LPing, Snakewood. In previous playthroughs I was struggling a fair bit to keep up with the absurd level curve. The only reason it hasn't been an issue this time around is because I found a glitch that let's me rebattle a boss. I have to abuse a glitch in order to keep up without having to do hours of grinding off wild Pokémon.
Let's be grateful that the newer games attempted to fix these issues. There are still some issues, sure. Black and White still have a bit of a problem with levels in the final areas. 8th gym's ace is 43, final boss's ace is 54, but it's nowhere near as bad as Diamond and Pearl. The Exp. Share is also too good in gen 6, and to an extent 7. Grinding levels is pretty much something that's always been a part of Pokémon, whether we like it or not.