As someone who used the S5II extensively - especially on travels - the moment I got my S9, the S5ii ended up staying at home unless I really needed the mechanical shutter. You might think that a S5ii with a Sigma 35mm F2 or a S9 with a 35mm F2 is a negligible difference, but in real life it really tipped the scales! And mind you, the only reason I own a Sigma 35mm F2 is because I wanted to shrink my kit for traveling - I usually shoot with the 35mm F1.2 from Sigma. But especially during the months of the year where I am living in Japan, where I'll average 15k steps a day, carrying that S5ii was definitely an uncalled-for workout! Even the smaller lens didn't change much, I found myself so often deciding against bringing my S5II due to size, weight and so on.
Only with the S9 did I finally find an option that allowed me to almost always bring a FF camera with me without having to think if it will fit a small bag or if I really want to carry that weight for 10k, 20k steps and son.
I didn't notice the difference in bit depth too much, but again, the situations I'd take my S9 instead of the S5II weren't challenging. Street, casual portrait, travel snapshots - I genuinely don't believe that the 2 bits more from the S5II would have been actually noticeable apart from very fringe scenarios. Obviously for proper landscape photography or in a studio things would've been different.
But for me, the S9 made an actual difference in how often I use a "proper" camera and it also replaced the S5II in many situations. I really think it's one of those "on paper" it's maybe 20 % but in real life it's much more than that situation.