I totally agree here but habitats are not meant to operate or compete on the same level as planets. They are meant to improve the latter by freeing up building slots making planets more efficient. Example is research focus habi (2-0-6-0 districts) with 3 building slots left after managing amenities, robo production (if you need any) and institute, plus 3 more housing to spare - a prime candidate for refineries (or fortresses - they provide housing too). And agri habi (I just checked, but as barbaric despoiler

) produce 132 food WITHOUT bonuses from 11 farms using 8 districts and housing 50 pop + 1 merchant at 0 housing left! That is a COMPLETE habitat. 51 pop here (just agri one) is a limit and this one if efficient! Meaning somewhere few planets are freed up from 11 agri districts. Even if those planets are food-rich, once I Voidborne (and I always do) I move that food production onto newly constructed habitat. Planet utilizes other type of districts or goes for ecumenopolis.
Ringworlds take too long to construct plus extra perks (not to mention the cost) to wait while habitat is an early solution that stays with you till the end. Later on just reshape it as you see fit to satisfy sudden demands. Use it as buffer for extra pop - they need to work somewhere anyway. Habitats also can help in robot assembling. The list goes on...
This way I don't understand how a 1 perk worth "half-planet" is not doing its job! Relatively fast to build with 100% habitability it is situational yearly, yes. But taking you out of that dire situation saying: "Here, take my hand. We make it through." doesn't make it great? An artificial space structure I always respect!