In my opinion, it would be better if you could choose between two or three monsters every time you open an egg. A tactical choice.
It is true that it would be easier to win, but you can always increase the difficulty.
Another thing: it is relatively difficult to get 4 monsters of the same type and the rewards are not well adjusted in my opinion: If you get 4 the bonus is doubled; I don't think it's enough. It's much harder to get all 4 of the same type than it is to get different synergies. In other auto fighting games every stacked bonus is a much better improvement than the last.