In vanilla CK2 as it stands religious minorities (which can only really be meaningfully expressed by characters, since CK2 is largely character-driven) are very easy to completely remove, which is incongruous with our understanding of history - religious minorities existed in courts and some courts/populations were heavily mixed (especially towards the beginning of CK2's depicted period). I think the move from auto-conversion to chancy-conversion influenced by character traits is a good one because A) it puts the focus on characters (is your ruler persuasive or learned enough) and B) it prevents the player from ironing their entire court one religion in a week.
Gameplay-wise it throws up approval challenges but not insurmountable ones (since you can still pass heretic-title-revocation laws, or take the tyranny hit) and I like the nuance of choosing how to convert - it adds a little bit of flavour to what is often a strategically-driven choice on the part of the player. I like differentiating between pragmatic queens who view unified faith as a political tool (and thus convert via diplomacy) and frothing-mouthed tyrants who incur the proper penalties for their repression. Like CK2+ at its best, it's a small choice that allows you to tell a story to yourself as you play, and I personally prefer that over "oh good, they're all 30 approval, let's clean house".