The whole point of this discussion is that decisions based on somebody's opinions but applied to everybody give poor results. In this case, if you forced "office Mondays", you would lose several seniors. The question is, is the net result worth it? You can be convinced it is, but without hard data it's meaningless.

(I work for an international corporation and we have hybrid meetings once a year but it never works 100% in person because people work from different continents, it would make no sense.)