Its more about what the sub adds to the sound in order to get loud.
the mtx jackhammer 22 may be loud but it sound bad to to it adding noise not intending to be there
the tantric md 24 is a balancing act it gets loud and still sounds good becauseit only adds a little noise
the Ia flatlyne 21 is sq based sub as it is vary quiet in respect to sub noise yes it still can get loud but with very little added noise.
The size of the sub doesnt carry any weight on how it sounds other than adding mass and lowering the fs of the sub. To much mass can create problems though.
most sq subs use bl linearity prior to suspension linearity due to suspension design limits. So a good motor design can go a long way over just a good suspension.