Evidence for UA is here and here:
https://wiki.tfes.org/Evidence_for_Universal_Acceleration
https://wiki.tfes.org/Variations_in_Gravity
Where?
Variations in gravity doesn't even discuss UA.
The closest you get is the equivalence of gravitational and inertial mass.
But that is expected by relativity, where gravity is the result of curvature of space time.
This also matches with the feeling of free fall.
The absence of a mechanism for gravity is not evidence of UA.
Firstly, gravity is a fundamental force of nature and it has a "mechanism" as much as any other force.
UA on the hand is not. Earth accelerating is not a fundamental force of nature, yet has absolutely no mechanism or justification provided for it by UA.
Pretending you have a mechanism by pretending Earth accellerating upwards is a mechanism is just distracting from the fact you have no mechanism.
That is worse than saying gravity is the mechanism.
Talking about the equivalence principle is not evidence for UA.
The closest you seem to get to evidence are your 2 tests of you falling and dropping a ball, but you just state the way you want.
A straightforward analysis is that Earth appears to move towards you, accelerating up to meet you while you are stationary, and that the ball accelerates downwards while you are stationary.
All it really measures is relative motion.
You know that in exp1 you move relative to Earth and in exp2 the ball moves relative to Earth.
We cannot see that Earth moves upwards, just that there is relative motion.
The absence of any feeling from gravity in free fall is exactly what is expected, and the exact same reasoning can apply to other fundamental forces.
Gravity doesn't need a power source. It isn't just dumping in an unlimited amount of kinetic energy. There is gravitational potential energy, which can be converted to other forms of energy.
Your addendum is also wrong.
Gravity does not behave exactly like Earth accelerating upwards.
Objects falling do.
Earth accelerating upwards doesn't explain why Earth orbits the sun, or the moon orbits Earth, or satellites orbit Earth or the variations in g across Earth, or gravitational attraction between other masses.
So where is the evidence for UA?
So far all I have seen is UA can explain why things fall just like gravity can, and you don't like gravity.