There's actually Japanese players on Splatoon 1 because it's not region locked and those guys don't fuck around so, overall, the players on the first game are definitely better.
And these "balanced and fixed" comments are bullshit (not you, but whoever says it is bullshitting). What they "balanced and fixed" was making the franchise more accessible and leveling the playing field. It's what Nintendo does. They release a game and then spend years tinkering with it until they find a formula where people of lesser or no skill can compete with people who are actually great... thus alienating the great players and forcing them to find something else to play.
When I play Splatoon 1, there is never a time where my experience and skill gets trumped by an in-game handicap. That is to say that every time I get taken down by another player, I feel like it was my fault. There is always a feeling of screwing up on my part. When I play Splatoon 2, on the other hand, it's almost constantly NOT my fault. The game was made that way. It's designed that way. And I just can't fucking take it.
It's the same reason I just can't handle Mario Kart anymore. I can't handle games that handicap players of skill so as to allow lesser players to compete. It makes practicing and actually putting in effort pointless for me and drives me bat shit insane.
Splatoon 2 handicaps skilled players? Please explain. I don't see how getting splatted is any less your own fault in Splatoon 2 compared to the original.
I haven't played the 2nd one but judging by the gameplay maybe they're referring to the fact that the game is less balanced due to a wider variety of weapon options. I've watched a match of Splatoon 2 with a recently added map and a player was spamming with a certain gun and going close to the opposite team's spawn point. It wasn't effective but they managed to still get kills. I don't think you can just do something like that in Splatoon 1.
I agree about the Mario Kart point though as I've actually played MK8. I don't understand why they got rid of wheelies, drifting on the spot, etc. Items are unreasonably balanced to the point where your skill on the track is hindered by item luck. I mean, you can get triple reds in like third place. There's no recovering frames when you get hit either, so you can get repeatedly demolished. As an MKWii player none of these problems existed. The only track that was garbage for competitive play was Luigi's Circuit. No skill required, all luck.
Meanwhile, in MK8 I can only find skill to be slightly favored in 200cc. But even then, 200cc is flawed since it functions horribly on a stage like Rainbow Road.