When I started RM2, it was with a group of players who had been together for years. Depending on the GM, the XP rewards would be all over the spectrum.
"You killed the troll, unlocked the chest, found the secret opening and you killed 3 goblins.... everyone gets 1800 XP."
or we had the "Flat Rate GM", the session was worth 900 XP. Didn't matter what anyone did, if you were there for the gaming session you were rewarded 900-points.
Occasionally we'd have a GM who put some calculation and thought into it and reward what seemed appropriate. As I started GM-ing and the years went on, I looked over the core XP system and started using it. It's not that difficult. I makes notes for each player as we go, I tell the players to track their crits, damage given/taken, etc. At the end of the game, I go over the events and ask the players to recount their experiences so I'm not trying to remember everything. As the PCs go up levels, you don't have to worry about the 1st time bonuses and so on, but those multipliers get them leveled up faster and they enjoy that. They are able to get out of the growing pains stage and have decently powered PCs after 3-4 sessions.
As a GM "gift of the gods", I also roll a D10 and give an additional percentage bonus added to their totals. Fate, the gods, whatever they believe in has smiled favourably upon the PC and granted them additional bonus XP.