Thank you everyone for the great responses so far (including the photos of many lovely basses).
I definitely agree that light basses are a struggle to play if they neck dive. I've played a Hofner-style bass in a recording studio and it was too light. Felt like toys and the neck dive was horrible; I felt like I was fighting the bass more than playing it. I've also read on TalkBass about people excited about the new pawlonia-bodied Tobias Growlers (many examples of 4's at
Sweetwater are under 7 pounds, they have long upper horns presumably for balance) but report that they neck dive because the pawlonia bodies don't counterbalance the necks enough.
I once had a 6-string whose ergonomics were as ideal as it gets for me with a 6-string and its tone was monstrous. I called that green beast Incredible Hulk. Thing weighed somewhere around 12.5 pounds, though. I could not shoulder it for more than 40 minutes or so.
I also once had a Spector Rebop 5 that weighed about 8.75 pounds (but felt lighter), but the compact body, bridge placement, and 35" scale made it balance too horizontally for my liking so the first position "money notes" felt like a miles away reach. The kinda chunky neck didn't help either. I could say the weight of that bass was ideal for a 5-string and the bass sounded tremendous, but its ergonomics didn't suit me.
And like others, my aging shoulder loves my 7.5 pounds bass but my 8.8 pound bass... I find its heft comforting, especially the way it presses just right against my sternum and my shoulder doesn't complain (since it balances nicely). A Fender Aerodyne I used to have (it was about 9 pounds even) pressed into my chest too hard, even though it was an otherwise ergonomically sound bass. I might put a set of Gotoh Res-o-Lites on my 8.8 pounder to move it a little closer to 8.5 pounds (which is close enough to my sweetspot) since that's the bass I reach for more often.
Ergonomics and weight are important for sure (whether due to age, medical issue, body type, etc). But I guess I'm like Baby Bear in that I like everything just right. Balance just right and weight just right (not too heavy, not too light). Heh, and also like Baby Bear I like my neck profiles not too skinny and not too chunky.
(And, for reference, I'm 47 now but I'll probably be singing a different tune when I'm 74).