Or we could internally (during the optimize() calls), explode this kind of condition into

X == 1 AND Y == 2 AND Z == 3

and then let the normal logic handle it?

Or is there something that I am missing?

The main reason why I don't want to do such explosion is a possible future optimization of conditions like (A, B) > (?, ?) in presence of an index on columns (A, B) to a proper index condition like (A, B) > value. It isn't possible right now, in this PR a shorter index condition A >= value.firstColumn is generated.