It was said of legendary bluesman Lightning Hopkins that he simply could never constrain himself to a traditional 12-bar (or any...) form, much to the consternation of his sidemen.
Famous quote: "Lightnin' change when Lightnin' want to change..."
One takeaway is: You've heard of Lightning Hopkins. The sidemen, not so much.
G's not getting his way and is acting out in maybe the only way he knows how.
This _could_ be a teachable moment if you can get him to acknowledge that he did not achieve his desired result.
Experience can be learned. "Experience comes from bad judgment." Ego is necessary, but pig-headedness is toxic.
G has probably never had to follow a fixed form or lead sheet. IMO, he'll need to learn this skill, which I consider essential for working well with others.
In my mind, there are multiple, separate roles, some of which can be performed by the same people.
1) Songwriter. (At some point, you must accept that the song is done and stop changing it, except to accommodate the arrangement).
2) Arranger - Decide song form -- 'A' sections, 'B' sections, Bridge... What instruments play what, when. When you have decided on an arrangement, this job is over.
3) Musical Director / Producer -- What the instruments should sound like, "feel" of the song.
4) Performers - interpret the song as it has been formed by 1-3.
5) The Business Side. Bookings and such. Until you have a product, this role is just generalized planning at best.
Until you can establish who is doing what and -- important point -- When That Task Is Done -- you don't have a foundation for performance recordings.
IMO, it's always desirable to record every rehearsal, even though I don't always do it.
To me, it sounds like your Songwriter wants to jump ahead to Producer but doesn't have the skills or the vocabulary.
Nor the maturity that comes of confidence that the song is DONE and stop changing it.