en passant is considered in current tablebases. It is true that castling is not considered because it is so rarely relevant for endgames and because the program using the tablebase can account for this with minimal extra compute time (it already knows if castling is allowed, and just needs to generate trees of when to do castling, with all other evaluation based on tablebase probes). It is also true that the method used for en passant would trivially handle castling, it has just been found to be uninteresting to do so.I'm wondering why you say strongly solved when en passant and castling (which are allowed in some positions with 7 pieces or less) are ignored from the current tablebases. Could you please explain what you have in mind?
So a more precise statement would be that current top engines using 7 piece tablebases can play any 7 piece position perfectly. And that existing tablebases technology could readily be extended to include castling directly. Or that existing tablebases directly strongly solve any 7 piece position in which castling is no longer possible.