? Semi-weighted is not synth action
YPG-535 is one of a number of Yamaha boards that uses their Graded Soft Touch action. It is not weighted at all. The graded sensation is not created with weights, but by increasing/decreasing the resistance in the sensors the keys hit when you depress them. It may or may not give you the feeling you're after, but technically, it is not a semi-weighted (or weighted) action. The place it misses your criteria is that it is a full keyboard with sounds, not just a controller. Though one can certainly just ignore its sounds, if one's "controller" needs are basic.
Personally, I find the distinction between semi-weighted and unweighted pretty pointless. Yes, the word does tell you whether or not there are any weights in the keys. But there are so many other variables that that, alone, doesn't tell you much about the action or how suitable it will be for your purposes (whatever they may be). I've played unweighted actions that have felt better (or played better for piano) than some semi-weighted actions, and vice versa.
76 keys will take care of what you need. I don’t think you would ever need the 8th octave. You will most likely Can play 99.9% of songs you want with only 76 keys.
88 keys is not just for being able to play any song. It's also to have more space for splits. Also, even songs that don't "need" all the keys can sometimes benefit from having them there for improv/leads.
When I was hunting keyboards, I tried quite a few "semi-weighted" actions --
. . . they felt like "synth action" to me.
The keys had no inertia.
Correct. Because adding weight to keys does not give you any piano-like inertia... inertia requires a hammer mechanism, which semi-weighted boards don't have. If they did, they wouldn't ve called semi-weighted anymore. ;-)
My question is: are there any 88 key controllers WITH hammer weighted keys that are not heavy? Like 15 to 25 pounds? Probably impossible.
Casio PX-5S? Not exactly a controller but I see it used as such by several folks in another forum.
Although it has sounds, PX-5S actually has a lot of MIDI controller functionality in it. Even without using any of its sounds, it can function as a 4-zone MIDI controller with 6 assignable sliders, 4 assignable knobs, pitch/mod wheels, and both USB and 5-pin DIN MIDI connectivity.
There are some other sub-25 lb hammer action boards, especially if you're willing to drop below 88 keys. But if you go up a little to the 25-30 lbs range, there are many more.