1) What is FFXIV as we know it but an admission of a horrible mistake?
No, that's ARR. FFXIV as a whole is not an admission of constant mistakes.
2) Caster potencies remained largely unchanged if that's what you're referring to? Else you're saying that the issue is not the issue.
Old SMN did high DPS, usually top 5, often top 3 if played well, and could out DPS a lot of BLM and some SAM players in the hands of a skilled master. Current SMN is not tuned to that, so if we got old SMN's rotation but balanced to do new SMN's damage (that is, if SMN's overall damage was unchanged), you'd be playing the hardest Job in the game but doing the functional damage of a MCH.
See above.
4) This doesn't seem to be a point with any substance.
No, but that wasn't a rebuttal with any substance. The point has substance, you just have no counter to it.
5) Hopefully they'd have made something that has gameplay, specifically gameplay in keeping with the summoner we've had for the last decade so the change wouldn't be as bad.
And if they haven't?
6) If they'd done it properly then it wouldn't be necessary.
But that's not the world we live in, now is it?
New summoner does scarcely better than mch damage, old summoner was an actual caster and did appropriate damage for such a role, ie upper half of the dps.
Exactly. So pasting old SMN into new SMN's spot today would make it a worthless Job no one would use unless they ALSO reverted the damage and balanced its damage to be boosted. Keep in mind it has no 81-90 level abilities for OLD SMN, meaning it wouldn't be getting the potency boosts and higher burst finishers that everyone else has. Thus it would be doing less damage than RDM while being harder to play than BLM.