Here's the thing, as a DM, I wouldn't give full experience for the Lich and Death Knights in the latest example. They would have an xp value as challenges when the situation is overcome unless actually engaged, and creative solutions (or funny ones) would earn a bonus. Regardless, the 5E advancement is off-the-charts too rapid.
I seem to recall Mike Mearls or one of his team at Wizards of the Coast, mentioning alternate charts that would be in the DMG. They have since stated that quite a bit had to be cut from the book before release, and I can only surmise the alternate charts were cut.
I imagine working out an experience advancement table wouldn't be that hard to do, it's the getting the pacing right that is the tougher part. And if I really wanted to as DM, I could just tell the players when to level. I much prefer tables, probably for the sense of reward I get from it as player and DM.
When I return to running Ptolus, I expect to have put together an advancement table more to my liking, that gives everyone time to explore the setting before being too powerful for almost everything.
Keeping the change simple is important. Considerations include changing just the advancement table; reducing the experience awarded for combat; figuring out a way to convert to xp for treasure with drastic reductions in creature xp value, etc. I'm currently leaning toward just the first option. This is something the players will be consulted with for input and ideas.
More time is still needed DMing the game before I feel ready to offer up additional house rules.