Leg extensions are the bomb. For me, it's even better than squats and deadlifts cause i have a bad lower back. Probably the same thing with you since you are arching your back in your deadlift videos. A PT at FF advised me to deload after every deadlift rep instead of holding on to the barbell so that it is less stressful for the lower back.

My current leg extension max is 75kg so far, while for squats and deadlifts it's still a sissy 60kg.

Not sure sp00ky coz different FF branches may have different equipment/brands/models. But I'm sure for me it's in kg coz if it's only 75lbs that would be about 34kg which i could lift easily with a single arm.