As for my own mod I definitely tweak AI for different factions - by religious anticipate and some other lore factors. But as for your project with only one AI label - this is the simple way to make one common decision for many cases. I just added it into my code and AI became much more active - before I had tested campaign in hotseat mode up to 840 turn and there were no defeated factions at all; after adding this - at 150 turn 2 factions was defeated.
Code:
<!--
3
-->
<min_entry is_target_faction_to_outlive = "true" stance = "Neutral"/>
<faction_attitude pts_desire="400" invade_priority = "1500" continue = "true"/>
</decision_entry>
It uses win_conditions outlive_faction parameter. I remember that you mentioned it's bugged and decided to try to play with it myself. So with this entry and any to_outlive factions in win conditions it makes sence very much without boring coding in descr_strat.
For my mod I plan to add more pts_desire parameters for more flexible AI behavior.