I think I know what he's talking about with leg press. The last time I had L5 issues, I had to stop squatting and went to leg press to take the strain off my lower back. When lowering the weight past parallel, I think the slight rounding from the pelvic area caused pain. It's not incredibly intense, and I was able to fight through it to get my sets in, but there was definitely noticable discomfort.
The machine I mentioned earlier has been a backsaver on leg days for me. I wish I had one of the pendulum machines at my gym. Looks amazing. Belt squat too.
I have this same issue with leg presses as you. I don't use the leg press often but if I do I only press with one leg at a time. my back is so sensitive to basically any vertical loading now and it fucking sucks. I used to do powerlifting so my ego took a hit when I had to give up heavy squatting and DLing (I loved them and am envious of those who are still able to do them). I lost quite a bit of muscle also but that's another story.
I got hurt in 2009 an i've been in pain ever since and not one day goes by without some level of pain. l2-l3 have a herniation. l3-l4 are bulging. l4-l5 bulging. l5-s1 have a herniation. I can walk so no surgery for me according to doctors. Pills and "stretch" or "oh you've tried PT, right?". LOL. Anyway, leg training has become a challenge for me. I gave up all barbell squats and deadlifting because of how bad I'd feel for days afterwards. not worth it for me at this juncture. ultimately, the compression causes me great pain (or too much than I'm willing to deal with now). even holding a 10 lb bar and touching my toes caused a pretty bad reaction.
So...take this for what it's worth, I'm no Mr. Olympia but these are the things that allowed me to get very good workouts and very sore with very little or no spinal compression:
deep bodyweight squats (hams make contact with calves) with no lockout and with heels elevated, 20 reps, 20-30 seconds rest, 10 sets. sounds easy. DON'T LOCK OUT and it might not be so easy.
Seated Leg Curl machine. Lying Leg Curl "pulls" on my spine a little too much. Standing Leg Curl or Kneeling are ok and I don't get much pain but I get a better stretch in the hams from seated.
Lunges. I prefer Walking Lunges and sometimes superset this with Deep Bodyweight heel elevated Squats.
Bulgarian Split Squat.
Sometimes I will stand on a high angled slant board and hold two DBs at my sides and again do deep squats with a very slow negative and try not to lock out. Do them slow and make the movement hard.
Sometimes I will use a Hack Squat and no weight or only put quarters on and do hacks Platz style where the heels rise off the platform and the knee move past the foot but be careful. this can be hard on the knees. Sometimes I will do half of my set in the Platz style and the rest of the set normal fashion but I always try to get hams to calves in terms of depth.
Pendulum Squat- I used to own one and I was able to fry the hell out of my quads. I love the movement! However, at the very bottom of the movement, the compression was too much for my spine. Again, maybe yours is different and maybe you have a different machine than I did (mine was by Paramount). Even unweighted, the compression caused me discomfort although my quads loved it. I also went hams to calves for the depth and I'm sure that wasn't doing me any favors but if you're not going to all the way down using a Pendulum Squat machine, what's the point? That's my take at least.
Belt Squat - ok movement, not much compression. depending on your build, this is more hip dominant. I couldn't rely on these to blast my quads because they kind of pull your hips back with the way the machine and loading point is designed. it truly does mimic a powerlifting low bar "hips back" (hip & glute dominant) squat. even when I tried to keep my torso upright w/elevated heels I still felt my hips pulling back and consequently, couldn't get the amount of quad activation I was looking for. Again, for a total lower body move, it's fine and shouldn't hurt your back; just not the best pure quad move IMO, just like how a low bar hips back PLing style squat isn't the best quad builder either.
Sissy Squats done properly (think "long lever" not just drop hips below like most do it; the long lever style will also work your abs hard but it
will fry your quads). You can do the long lever style and then once fatigued go into the style that most use where you just lower your hips while the tib and ankle remain locked place via the Sissy Squat device. This will work well for quads.
And finally GHRs are good for hams too, again, again think long lever and try not to push your hips back too much when coming out of the bottom. Use a band if you need to. For pure ham focus w/GHR, much or all of the movement should only happen at the knee. Again, think "long" lever and it will also work your abs statically.
I don't have a ton of workouts using the Reverse Hyper only because I haven't had access to one regularly but when I did I didn't find it to be Earth-shattering. Maybe I didn't have enough time on one. maybe they will work well for you though.
Calves shouldn't be issue as long as you stay away from heavy Standing Calf machine.
Also, the first movement I ever dropped was Bent Over Rows. Those hurt me right away after my injury. I'd switch to Chest Supported Rowing movements asap. Those are still no doable for me even with an empty bar. This position itself is problematic. Just my experience, again.
Finally, if you are strict and honest you can train your lower body hard without heavy vertical loading. It just takes patience, discipline (keeping the movements strict and honest), and lots of reps and long sets (basically patience). I'm no expert but that's been my experience as someone who slowly had to remove most of the more popular exercises from their regimen to avoid being in bad pain all the time. Good luck.