Not true, you are fooling yourself. Machines are moving on a specific plane, the body may not need to struggle with forces of balance ect. It's been proven over and over free weights , barbells, kettle bells, dumbells and even some cable use assistance muscles can increase range of motion , even then standing is more functional than sitting. Although isolation has its purpose in training and rehab. You may want to do more research and train.
I've done both over long term comparisions, been training for 20 years plus, just sharing what works best for me.
when you mean proof, what do you suggest by that? and I dont' care about the functional stuff, the look results, are all that matters. The strength from machines does transfer into other aspects of life also, not as much as compound lifts, but again, I don't care about that.
also with cables there is room to lift, feel the weight differently, it's not just a straight line of pull. also range of motion for a muscle and an exercise are 2 different things, why do you think pro's use what most call "limited" range of motion, they do it to stimulate the muscle, not earn braggin' rights on how much they can use in full range of the movement.
now you seem to know your stuff, your avatar pic is good, just explaining why I think this, and not so long ago, I would have said the same you are saying here. I chose to open up my horizons a bit, and it's working.
I like both methods, but I used to kinda snub the guys doing what looked like lots of machine work, fast, incomplete looking reps as well. But this way of training,you can get in lots of sets without burning the cns, especially worrying about balancing the weights, you focus on what's important, stimulating the muscle.
This is part of my ever going research.