It comes down to complexity.
In this article, M:tG desginer Mark Rosewater dicusses the ten things every game needs. I want to focus here on point seven:
Strategy comes from complexity, or depth. The greater the depth, the more long-lasting an appeal your game has. You can have too much, however, because the greater the depth the greater the mental load on the player. How much load is too much load varies between players, and even for the same player at different times. Sometimes I want to play Trickerion, sometimes I want to play Kingdomino.#7) Strategy
There needs to be something in your game that allows players to get better over time. The reason people like playing games again is that they want to use knowledge from past games to do better in future games.
Combos (hey, look, it's the topic) add depth, or strategy to the game. By our original definition, they give you something you can get better at over time. But they also add mental load, it's more to think about during combat. To achieve the widest appeal, you want powersets that have combos, and some that don't, and the ones that do should vary in complexity. That way, players have a choice - they can pick the character that has the complexity they want at that time.
To use League of Legends as another example, the two most recent champion releases were Sett , who is very basic gameplay-wise (literally walk up and punch people) and Aphelios who has to have a completely different in-game UI because of the complexity of his abilities and their interactions. Again, those are back-to-back game additions. This isn't a case of, "we're getting better at this so we're adding more stuff to our champions", it's that Riot know different levels of depth are needed to appeal to the widest audience.
So yes, I would say powersets with combos are needed. Powersets that combo off of statuses inflicted by other powersets are needed. Maybe long-term things like animation cancelling could be a thing, even.
Again, though, I will stress it will be optional - not every film can be Inception, everyone needs a turn-your-brain-off popcorn flick from time to time. There has to be a choice of strategy and depth.