did you paint the joints? if you did, maybe it added thickness to the joints so they are more sturdy.

Ball joint made from what? If polycaps ball joint you cant fix it except use something like paper.

If ball joint made from PS and ABS plastic, then you need to add more layer on it. Paint the joint part to fix loose problem sometimes work but I suggest to use putty as layer on ball joint. Sand it if too thick.

Do not use hobby cement, it is not add layer on plastic but instead melting it. I use putty on ball neck joint for my HG Unicorn before. It works better than layer of paint.

Different situation. Seam line removal is bond the plastic together by melting it.
Doesnt work well for tightening joint which we try to add another extra layer on it.

Heck the normal super glue work best than hobby cement.
Use hobby knife to trim it first and then sand the part gently.

you can recarve or deepen the details lost if you know how they look like. with a hobby knife.

I really would like to digress from this issue now. I've said multiple times that it can be done but not as first or popular option that would first come to mind.

Clearly there are many variables involved from person to person, but I'm staying in the 'can do' camp and I've explained why it can be done. Simply put, the issue is whether it can, not that it should.

I'm going to ignore any post next that still imply or express that this is the only method recommended and used to fix loose joints.

Oh about the cement, I was comparing it to the Mr.Hobby Cement Deluxe, I find the drying time and viscosity very much the same with Tamiya Extra Thin.

If you want chubby looking Gundam, and since you already have RG RX78-2, you will be pleased to build RG MKII. There are two versions, AEUG (white) and Titans (dark blue), the AEUG would look chubbier due to the by brighter color.
Depends on type of glue, if you use viscous type (like UHU), it may take several days for it to truly garden.

Thin glue type like the generic elephant glue would only take a few hours to harden. Cement would take a day to do that.

If you don't want to use permanent solvent method, just put some blu tac on the joint.