It's just not a very natural movement on a smith. The body does not move in a straight line ever...period. The smith machine is exactly that..a machine. It removes core stabilization as well as the effort to stabilize the prime movers. Let's take squats for example. Core work? gone. P-chain work? DRASTICALLY reduced. So what does this mean?
Free Squats >>>> Smith Squats
Also
Free lunges >>>> Smith Lunges
In every instance you are doing more work and getting more done by using free weights as opposed to the Smith. There is no reason to use the smith over free weights. Some people say it is safer. The word "safe" is a relative term. The first time I hurt my back seriously it was on a smith machine...doing squats. My back hasn't been right since. I've had to take off countless weeks due to reoccuring back pain or pulled muscles. But that's another story altogether.
Are you working out one leg or two now? You mentioned squats and hack squats as well...Can you do bilateral leg movements or is there a reason you mentioned one legged movements?
BB hack Squats are fucking cool, have you ever tried them? They are hard!!
DB or BB lunges are great! Since you aren't using a machine you can do different variations 2. Reverse lunges, walking lunges, cross body lunges, lateral lunges, dynamic lunges. etc.
Sorry for all that....but you did ask for me to elaborate!! lol