Three or four books as a core seems pretty normal to me. E.g. Player's Handbook, Dungeon Master's Guide, Monster Manual. You could drop the monster manual if you plan to have stats for the creatures in modules and campaign books, but then you have modules and campaign books. I also have Mage The Awakening on my shelf, but it relies on the separate World of Darkness rulebook, and neither of them have any meaningful amount of information about creatures etc. And I have GURPS, I'm not going to count but it takes up more than 2' of shelf space....
No, I think what people object to most in RM is that you need to look things up on a table any time you make an attack (potentially twice), cast a spell (potentially twice), make a moving maneuver, or try to resist an effect. In 1st edition D&D, you also needed to look at a table to make an attack (once) or resist an effect, but already by 2nd edition you didn't need a table for attacks, and at some point (also 2nd edition?) you didn't need them for saves either. RMU does basically remove the need for tables for casting spells, making maneuvers, or resisting effects (there are tables that give examples for partial and absolute successes but they are really optional) but at the end of the day there's still going to be pages of charts for attacks. We've decided that's worthwhile for the detail they bring, but it's always going to be a hard sell to someone coming from a system where that was not required.