> temp tables don't spill to disk
my setup is local nvme ssd raid, so I hope this part won't be bottle neck. Also, if you are doing heavy join, where join order and method is need to be controlled, you temp table likely will be large, so you will need to be ready to have disk io.
The same is of course true when you have big joins that don't fit in work_mem but default size of this will be much larger.
I can usually fix bad plans with CTEs, no need to get much fancier. And the problem is often caused by schema design where you have a mapping table of two tables in the middle and your join is N-M-M where the planner has no information about the relationship between the two outer tables.