It is obvious that a larger sensor receives more light. If we assume that the non sensing electronics per pixel (you mentioned) shouldn't need to get larger as the sensor gets larger, then larger sensors obviously have significantly more area available for light sensing than small sensors.
Of course, they don't have to use it - but then why use a larger sensor?
Plus - we can clearly see that most cameras with large sensors have both better noise levels, and better resolution (even at the same pixel count) than smaller sensors. Lenses also cannot have infinite resolution.
So, no - that is not snake oil)
Lens characteristics also affect smoothness of bokeh. You can see this by looking at the edges of out of focus highlights. Lenses where those are soft will result in smoother bokeh. Hard edges result in less smooth bokeh
Both of these phenomena are measurable.
I'm sure there is snake oil in photography, but the two items you mention are not that - and I can't think of any definite ones off the top of my head. We definitely don't suffer from the likes of magic crystals to put on top of the camera, or $10,000 cables to connect camera to computer.
I just ran through sensor lineup of Sony:
Sony Semiconductor Solutions Group develops device business which includes Micro display, LSIs, and Semiconductor Laser, in focusing on Image Sensor.
www.sony-semicon.com
The important thing is pixel density characterized pixel size in microns.
Now I took 20MP M43 sensor IMX272/269 which is probably in my camera (Olympus EM-5 MKIII), and compared it with IMX410 which is fullframe sensor. Notice the M43 has pixel size 3.3microns while FF sensor has 5.94microns.
So DPReview has database of sample photos in their reviews, where you can select particular cameras:
It says Olympus on the front, but the OM System OM-1 is about the future, not the past. It may still produce 20MP files, but a quad-pixel AF Stacked CMOS sensor, 50 fps shooting with full AF and genuine, IP rated, weather sealing show OM Digital Solutions' ambition. See what we thought.
www.dpreview.com
I compared OM-1 which has Sony IMX472 with EM-5 MKIII which has sony IMX272 or 269 (just different interface, otherwise same characteristics), and compared it to 24,2Mpix cameras by SONY - Alpha 7 III, which should have their IMX410 sensor.
Same manufacturer, same lineup... Alpha 7 III is clearly better as both sensors used in OM/Olympus cameras. But pick different camera by Sony with higher pixel count (I took Sony Alpha 7R III which has 42.2MP sensor). You would notice that the noise is getting worse with higher pixel count, regardless total sensor size - because of smaller pixels. Also for some reason many other 24.2MP Sony cameras are really not on par with A7III in terms of noise.
Unfortunately things are even bit more complicated. I have been noticed by an astophotographer, that different sensors "gear up" on analog signal amplifier at different ISO settings. For IMX272/269 its on ISO 2000, but for IMX472 its on ISO1000. Due this my EM-5MKIII has lower noise on ISO2000 than on ISO1600...
For me... going from IMX272 to IMX472 isnt an upgrade. The noise is practically the same. The sensor use 4 photosensitive pixels instead of 1, but the net gain in terms of quality seems to be 0. It is true though that newer sensor allows higher native ISO.
Also amount of light... Solar panels can be enhanced with lenses to produce same amount of electricity but utilizing much less photosensitive surface. This technology is already used in microprisms or microlenses which focus light on photosensitive part of pixel. But given F2,8 at 1/125s, and pointing at white surface, amount of light exiting the lens should constant and has nothing to do with sensor itself. Yes, different lenses are made for different sensor sizes, but the F value nor exposure time are not characteristics of sensor. Only ISO is.
Also regarding bokeh... My point was bit different.
I can pay lets say 1400 dollars for M.Zuiko 45mm PRO lens which is weather sealed, and fully automatic. Or I can pay same amount of money for manual lens, without any weather sealing. Bokeh is used for marketing, so people forget what is the rest of the product they pay for.