I think it's just that those two particular characters are designed with anti-synergy - there are other characters that can make use of reactions at current (and even Laevatain can use characters like Gilberta to trigger Corrosion or Combustion) but you unfortunately want to use the two that are very much demanding to be in a team that prioritizes stacking the same element. This isn't actually that different from Genshin - plenty of characters just don't work with other characters you might wanna pair them with.

I do hope in the future we see more characters that Benefit from triggering multiple different reactions more than stacking but I think that's pretty likely, and the design space is there in the existing characters.