At this point I’d say half my collection of 8,000ish is mono recordings. 78’s, microgrooves, and some lps and 45s. If it was recorded in mono, it should be played back in mono. With repeating others about setup and cartridges (I use Miyajima carts and SUT for all mono playback), what hasn’t been mentioned is the room setup. I have 1 room setup for stereo and a separate for mono. In the mono room I have 8’ between the rear wall and the speaker and use open baffles. The result- the deepest soundstage you can imagine. While stereo imagery is impressive, it feels fake compared to mono imagery. In the mono room you at all about front to back. My point being, mono doesn’t really impress me in the stereo room - so if you have a setup already optimized for stereo, the setup may be the issue.