In regards to lower upweight due to escapement.
I think I may have contributed to a confusion that I have myself fallen for in the past and even until recently. I was thinking that when you are holding the keys down, they are lighter than usual, hence it's less tiring for you to hold the keys down.
Well, let me go back in the past where it all started and when I wrote that other post on PW. I have experimented with the Cybrid to remove escapement and just make the piano behave like a digital piano action: you press the key fully down and it lifts the hammer fully up without escapement. In order not to break things, I set-up the rail so that it's at the exact same height at which the key pushes the hammer. It's still a dangerous thing that can break the shanks, so I was careful. Long story short: the action suddenly started feeling exactly like a digital, i.e. tiring to play and pushing against your fingers.
So, I started analyzing why that is and thought that since the hammer is locked by the backcheck and still disengaged from the jack, hence bypassing the 1:5 leverage, then holding the key at the very bottom suddenly makes it lighter than usual and easier to hold. But I forgot that there's the double-escapement lever pushing the hammer up (even though it's held by the backcheck and not moving), so it's the equivalent upweight applied to the key.
And yes, I just measured the upweight both at the bottom of the keys and above the escapement. On my N1X the upweight at the very bottom is slightly higher than above the escapement. I believe it's exactly because of the double-repetition lever spring.
HOWEVER! It's important to realize that the actual effect of making the acoustic piano action tiring to play by removing escapement is still a valid thing.
So, it's still because of the escapement and we need to seek the explanation somewhere else. I believe it's not in the static behavior, i.e. not in the static upweight. Although, as you confirm, due to the friction, it's lower than downweight which helps. What I think the actual reason is this: the hammer gets detached after the escapement. This is usually 1mm before the key hits the bottom and also 1mm before the hammer hits the string. (It's also when aftertouch starts) Because the hammer is moving 5 times faster than key at that point and since they need to travel the same distance of 1mm, logically the hammer will be able to rebound and be caught by the backcheck while the key is still going down and that acts as a natural dampening of the key, but what is more important, due to the backcheck the hammer gets stopped immediately, with no jerk or additional rebounds. In other words, the hammer stops in a single motion which coincides with the key still moving downward, hence acting as a cushioning to the key as well which is a single smooth stop motion and at that point there's no residual momentum or energy.
Compare that to a digital piano where the key hits the bottom cushioning at the exact same moment the hammer hits the cushioning. Even if you hold the keys, you would still be experiencing the shock of these two hitting a semi-springy cushioning that acts against your fingers AFTER you've hit the bottom. And then, if you play fast passages without holding the keys, the rebounding hammer will push strongly against your fingers in a punching bag manner. I really believe the latter is the phenomenon many people describe about digital pianos "pushing back against your fingers". On a well-regulated acoustic, even pianissimos will result in hammers being caught by the backcheck thus stopping its motion without jerk/shock, in a single decelerating motion while the keys is still moving down, thus cushioning your strike.
