As far as competitive play goes, the games are quite different despite how similar they might appear.
Splatoon 1's meta was dominated by a specific top tier of weapons at it's highest level. Across the board, most weapons weren't good, but your cherries, sloshers, zimis, crbs, etc were all excellent.
Splatoon 2 (as of 4.7.0, hopefully they dont **** things up later) is very balanced across all weapons, barring some weapons that are still more or less useless. Things like the mini and slosher may stand out as strong, but overall you can make a lot of different team comps work with the right strategy due to how good most of the specials are.
When you factor in the QR meta of Splatoon 1 with the dominance of bubble, winning multiple fights and individual play is a lot more important compared to Splatoon 2 which has more room for unique comps and setups with multiple specials. Even among the "top tier" weapons, it is usually not worth it to go for individual outplays in Splatoon 2. In contrast, Splatoon 1 top tiers like the crb had multiple tools that allowed it to take fights, and the reward for winning was much higher.
The games function pretty similarly in a lot of ways, but they are still very different and difficult to directly find a "better" game