Assisted forms ultimately "assist" you at some fixed point which alters the path you would take if hanging, often removing your core entirely.
Also, I'd take the non-linear resistance of bands over the absence of core activation from a pull-up machine or the very different lat pulldown motion.
For reference, I'm a rounding error away from 50 and I still do advanced bar work - muscle ups, archer pullups, pull overs, etc...
I think it's important to always work with your bodyweight.
80% of strength is neuronal coordination, you'll get strong with the way you train.
Use your bodyweight in closed kinetic chain [1] exercises and avoid the machines unless you're injured or have a specific reason.
There are progressions for every level.
I recommend "Be your own gym" and "Overcoming Gravity" for great references on bodyweight training.
(Also: don't do muscle ups. The only people who like that are sports medicine docs.)
[1] https://en.m.wikipedia.org/wiki/Closed_kinetic_chain_exercis....
IMO, the best thing is if you have access to an assisted pull up machine or lat pull down.
Bands can work alright (and they're cheap!), but assisted pull ups and/or lat pull down allow you finely tune your progressive overload. The general problem with bands (and spring type resistance in general) is that the non-linear resistance makes it more difficult to judge your progress.