Saying Nick Brawl has too much 90s content is like saying a Sega crossover has too much 90s content or a Dreamworks crossover has too much 2000s content. The 90s were Nick's peak in terms of cultural influence, especially when it comes to cartoons given their high expectations and quick cancellations post-Spob. I'd frankly be more surprised if 90s stuff didn't take up a majority of the roster.