How did they manage to get big in the old days/before squat racks existed because my best gains have come from barbells and 3-5 x 5[/quote]
By actually trying.
It seems squat-free workouts are a load of BS (even deadlifts won’t make your legs big to the extent of squats as you’re not fulling bending the knees). I swear by them. I don’t know how those with knee problems/in a wheelchair can gain mass[/quote]
But my arms are still weak as I can’t chin or dip or do a handstand.[/quote]
Your arms are not involved in a chin or a handstand. The handstand is more balance and core, the chin is mainly back. The dip is the only exercise that requires a good bit of arm strength.
There are an enormous amount of resources online teaching you how to do a chin-up for the first time. I suggest you go read them.
Assume you gain momentum once you hit bodyweight? Or is it the opposite, you gain momentum and slow down once you hit bodyweight?
Neither. I have no idea how you came to anything close to this reasoning.
Most people who actually try can get to squatting 250-300 or so within the first couple months of training. Gains will slow down quite a bit after that.[/quote]
Chin ups use the biceps to bend the arm and handstands involve the triceps to keep them locked out
and with the last point, I assume that those peoples’ legs got much bigger. Did the majority of those gains come before or after the squatted bodyweight?[/quote]
You really are missing the point. Squat, deadlift, eat, sleep. Your legs will get bigger. There is no magic set point of your weight that you gain more mass. Once you learn your own body you can really see results. To do so go train hard and eat hard for a year. Take some before and after pictures for yourself. If you did anything right in that time you will gained some mass.