Even with older lenses the question is whether you can see the "lacking" resolution on the final product or not.

It depends on the printing/display medium. At every case, downscaling a higher resolution image pays off. Especially, if it’s a nice monitor for wallpaper use or a big print for wall display.

Absolutely! That is actually the only "issue" I have with my cameras, both are 12 MP. Don't het me wrong, they make great pictures, small file size has a bunch of advantages and I prefer to get composition right in camera anyway. But sometimes, usually for wildlife, you need to crop because even a 720mm equivalent lense only gets you that much of a bird in far distance inframe. And then low MPs only give you that much MPs and details to work with. But hey, I still get some nice shots, and most of the time I do landscapes and architecture anyway.