Custom ideologies are a little bit overpowered, it's true. I almost wish there was a point buy system or something so it didn't feel quite so cheaty -- you can just make your colonists research fast, not care about eating insect meat/cannibalism/seeing dead bodies/organ harvesting, etc, with no downsides. On the other hand, Rimworld's been pretty lax about letting you disable events you don't like, and now you can even just disable whole factions, too, and I guess the difficulty has always been something you opt into (whether with the literal difficulty setting or just picking harder biomes).
Regarding defenses, it's always been an arms race between players who find the most meta strategy that enables the most efficient defense vs. Tynan adding new enemy types and behaviors to counter it, so I don't have many complaints there -- I probably spent 300 hours playing Merciless with mountain bases and killboxes and manipulating insectoid spawns to completely avoid any losses which was... fine, but I've honestly had more fun lately playing with the difficulty dropped down and engaging with the combat system more rather than just playing tower spike trap defense. I remember way back when light affected accuracy and you could lure enemies into a a well lit hallway while your colonists opened fire from their shrouded bunkers, those were the days.
Anyway, I think the problem is a lot of players want the illusion of difficulty while actually not struggling at all, just look at how popular embrasures are despite completely trivializing combat. Fundamentally, Rimworld is designed to screw you over and is inherently arbitrary: there's no simulation going on to determine whether factions can actually afford to send raids your way unceasingly, it's just a function of colony wealth + time + a little RNG. The mods that try to address that (e.g., Faction Resources) are underwhelming.