I second that. It is so stupid to get a 6 stat monarch, only to hit the power limit. And before you start, i did spent every single point i could.
Why don`t PI make a simple solution: The monarch power cap is equal to the hardcoded ceiling, OR the price of tech, whichever is higher, so you could always spend your points on something, and not just loose them because you got "lucky" with great monarch.
Plan ahead and og an military idea route if you think you will bath in military points. This is an important part of your long term strategy.
You can get a monarch with good stats in many categories, and idea slots&buildings are not infinite.
I had a situation where i was at 999 admin points, 999military points, my 3 idea slots were fully filled, 3 stability, everything cored, and i was 2 ADM tech away from next NI slot, and next level of ADM tech costed like 1300, military tech 1200, since i was so far ahead already. Oh, and i had like -200 relation penalty for agressive expancion.