Pokemon that don't see much use is more of a Competitive/Userbase problem rather than a general Pokemon problem, and it stems from people not thinking outside the box. Like it or not, the Smogon mindset has seeped into the actual games to where online you almost always see the same sets on the same group of pokemon in the same tiers, not once being original. In fact last time i saw any sort of originality was a X/Y Triples "Round" team in which a user whom used a Blissy, Sylveon, and Jolteon (I forgot what the other three were) completely fucked my team up only using that move. It's gimmicky, sure, but at the time, and even now, shit like that was/is rarely ever seen.
Just look at Delcatty. BOTH Smogon and Serebii shit all over the poor thing calling it one of the worst Pokemon ever. I don't believe it deserves that label, as it has gotten little bumps here and there to make it useable.
- It gained Wonder Skin as a hidden ability in Gen 5, which is better than Normalize and Cute Charm. You can either combine it with a accuracy-lowering held item (Bright Powder/Lax Incense) or use a boosting move to take advantage of the opponent's Toxic/WillOWisp/ThunderWave not working, or both
- It gained Cosmic Power as an egg move in Gen 6, which combined with a HP recovery held item (Leftover/Berries) can keep it's longevity.
- Adding to the two points above, if it DOES get statused, It's a normal type that knows Facade, so you can fuck shit up and not worry about going down in one-two hits thanks to Cosmic Power (or even the attack loss from burn)
- In Gen 7, it gained 20 points in the speed stat, and can learn Stomping Tantrum, so Rock/Steel is not a huge issue anymore (it's only other options were Wake-Up Slap and Rock Smash). So that leaves you with one other move slot for either Ghosts (Sucker Punch), or Fighting types (Zen Headbutt/Play Rough)
Instead you see things like Normalize Thunder Wave because Electrics and Grounds can't immune anymore (which was fine in past gens when 1. Ghosts weren't as common as they are now and 2. you didn't have too many options back then), or special focused Calm Mind movesets... even though the special attack stat is the WORST stat on this thing.
There's even a blatant bias against certain other pokemon. Someone wins VGC 2014 with a Pachirisu, which IMO is the biggest inspiration ever in regards to "low-tier" Pokemon can dominate just as well as anything in OU, and Serebii still shits on it in it's PotW segment, basically boiling down to "yea, I guess it did good... but you STILL shouldn't use this thing seriously at all!"
Region variants and mega evolutions are nothing more than a "band-aid" that only covers up a problem that GameFreak didn't even create themselves. Alola Raticate??? "Oh hey, now he's FAT, and has better defenses and can take half damage on ice and fire attacks" yea ok but he's normal/dark now, which means double fighting weakness (4x instead of the 2x from the original), so all of that is moot if he can go down with one hit. You essentially made a WORSE Raticate considering there was literally nothing wrong with the original one. Flame Orb Guts Raticate with Protect/Facade/SuckerPunch/Stomping Tantrum with 252 Attack/Speed fucking owns a lot of shit.