There’s this prevailing wisdom in the forums that defaults pretty much everyone to always work on your 4 star heroes no matter what. While I understand their reasoning and thinks it works in a lot of cases, I think it isn’t so absolute and we need to go on a case-by-case basis.
None of your 4-star yellow heroes are amazing (there are very few good yellow 4 stars that are easily available); on the other hand, poseidon is a great hero.
Sure, 3/70 5-star heroes are generally weaker than 4-star heroes. But Poseidon is an s2 hero that has higher stats by default, and, even if he’s weaker for a short while, he has much higher potential later on.
I think that the tiny bit of benefit in the near term does not nearly warrant everyone to always work on 4 stars, pushing back their 5-star agenda for years, potentially. It hardly makes sense in terms of absolute game play, and it makes even less sense considering as a player, I think many of us are attracted to obtaining at least a couple of those ultimate, maxed 5 star heroes just for the fun of it.