Rather than ratchet down monster kill XP, consider DMG pg. 261 and its notes on rewarding XP for non-combat challenges. If there is parity between the three pillars with regard to what is rewarded XP-wise, then the players can just do what they want at any given time and be rewarded regardless of approach. Discovery of the character is good fodder for transition scenes. These are scenes in between moments of action where the PCs are resting, planning, travelling, etc. It's a good time to pick on someone who hasn't had much spotlight time up to that point in the session. The DM can pose a question about that character relating to backstory or their thoughts/feelings on the events of play. Then through interaction, the players engage as their characters to figure out the answer. Once the answer is discovered, DM rewards XP and the next scene begins. One or two of these a session, session after session, builds a lot of context and encourages development. I've found for it to work well, the players need to be able to claim it for themselves. So what I do is if the players voluntarily take disadvantage on a roll the DM has asked for and justifies it with a trait, ideal, bond, or flaw, they can take Inspiration. Alternatively, if they act in a way that creates a meaningful setback or cost because of a trait, ideal, bond, or flaw, they may also take Inspiration. For example, Chuck is forced to make a hard choice between helping a friend and saving a valuable NPC. If I decide to help the friend, I can say "Chuck is loyal to his friends, not to any ideals, and everyone else can take a trip down the Styx for all I care... that's his ideal and worth Inspiration." Then the NPC dies or whatever, but I get my Inspiration. The DM just vetoes it if it's lame or a stretch. Mind you, players acting in good faith don't seek to do that.