A shock can be completely empty of fluid and nitrogen and it will not cause it to squat, that's 100% the job of the spring. The fluid and gas charge is part of the dampening system. If it's not sitting at the correct height or not able to be set to the correct sag, its a spring or spring adjustment issue. Without yje spring a shock will compress under load and not return and a shock will hold weight without and fluid or charge if the spring is in place, there will just be no dampening. Take a few minutes to read up on how suspension works before you start spending money.