Theres no such thing as a '4th choice'.
Its about partnerships + you cant play Keane and Mina together so zouma/holgate and Mina/Keane are the choices.
Well we don't know if Mina and Keane can play together or not, Zat. There's no evidence either way.
It's a safe assumption that both of them are similar in terms of their strengths and weaknesses, yes, but we don't know for sure.
It's why I'd try it out against Brighton. If it works, ace, although Chelsea would obviously be a different test yet again. If it doesn't work, then we know that maybe we need Holgate to come in for that game against Chelsea.
It's a tough balancing act but against Chelsea I highly doubt we'll play a high line. It would be criminal to do so against a Sarri side regardless, and especially given Hazard's form, so Keane/Mina's lack of pace may not be much of an issue.