Own 4 marlin X rifles: 7mm-08. 308w. .223 and a 25-06 that's now a 7x57. Rebarreled the 25-06 simply because I wanted a smaller case cartridge....it shot well when a 25-06 as have all my Marlin rifles. With right load, expect them all to shoot 1/2-3/4" 100 yd groups. Matter of fact, took the .223 to range this morning and one 4 shot 100 yd group was 1/2", with three of them in basically the same hole.
Anyway, first thing I did after trying one of my Marlins was to do as suggested before....make the barrel free floating and reduce the trigger pull by adjusting it lighter. Worked for me. But as mentioned earlier, perhaps you just have one that will not shoot well.
Occassionally run into a fellow shooter at range with a Marlin X rifle. Like me, theirs shoot quite well for them.
Keep trying.