He may have those awesome defensive stats....but he’s not so good. He lacks recovery as well as a good movepool, and Rock isn’t a great defensive typing. He has a decent 100 attack and a decent offensive movepool, but his speed is bad, his 100 attack is outclassed, and he is outclassed by Rhyperior in Trick Room.
Same with Regirock, he has good defensive stats, but no recovery, not so good movepool, and horrible defensive typing. His offensive movepool is fine, but again, bad speed.
He’s a bit better than the other two, sporting the awesome steel typing and a good 150 on both defenses. He’s fine, but is outclassed by Ferrothorn in every single way.
The best Regi. The amazing ability in Transistor, one weakness, the Highest speed, and decent offensive stats make it quite the strong Pokémon. However, it’s movepool is atrocious. Overall, it’s a solid Pokémon that I would recommend.
After seeing that 200 HP, you’d think this thing would be a wall. Wrong. HHe has the great ability in Dragon’s Maw, the awesome signature move of Dragon Energy with 150 base power, and access to Dragon Dance. He also has good 100 attacking stats. And same with Regieleki, he has a sad movepool. Atleast you have Crunch, Thunder fang, and Fire fang if you choose physical. He has a mediocre 80 speed, but this can be made up for by using a Choice Scarf (preferred if you use Dragon Energy) or by using Dragon Dance. Overall, it’s the next best Regi behind Eleki.
Ah yes, the king of the regis. He has amazing stats. He also has a nice movepool to work with. All seems to go well for him until you see Slow Start. It halves his Attack and Speed stats, basically eliminating his offensive capabilities, for 5 turns. You can try to stall it out with Protect and Substitute, but it ends in you being injured (unless you hold leftovers, and even then, you can’t have an item to help him damage if you use them). Stalling it out also results in you having 2 moves to attack with. However, you can use him in doubles with a Weezing with Nuetralizing Gas to eliminate slow start, or you could skill swap him a good ability. He does awesome without slow start, but that would mean having to have a Pokémon to help him. Overall, he’s not that great.