I will try to keep my responses brief for digestibility.
1. I said I hadn't played BLM often enough immediately before or after a SMN at the same ilvl to compare their metrics as well as I'd like before attempting to pinpoint their points of balance. I never said I had few hours on Summoner, which to me is what matters a hell of a lot more than whether some sense of job "loyalty" prevents me from playing anything else seriously. When raiding, I tend to play what class seems to suit the fight, or the tier as a whole, best given my surrounding member's composition. I'm a fill. That said, I suppose I will have to trust my experience on a BLM, regardless of allowing my SMN to slip ahead in ilvl, a bit more than I trust that of yours with a BLM at 57, even as clearly insightful as you must be to have determined that raid design's movement requirements have made BLM inviable without having stepped foot in a single HW raid on said BLM.
2. I don't see how you can go out of your way to poke holes in BLM's design over its dependence on turret-time and then say that niche differences can be forgiven due to the two caster classes' skillsets "complimenting" each other. To me at least, the caster role in general is known to have superior AoE skills, and this has been the case throughout XIV's history. However, I don't see why the Summoner and Black Mage should need be diversified by whether or not they're "battlefield control" mage or a "one-on-one" mage. Differences in the timings by which AoE or ST damage is output seems plentiful variation; enough to make the jobs feel different without forcing either into an isolated niche. Your proposed "harmony" suggests a consistent double-caster composition, but this is rarely the case; more often, casters are forgone outright at high levels of play in HW unless their LB is specifically required. Were your classification of AoE and ST mage truly the case, one would be taken only to certain fights, and then further fade from the majority of those fights, too, as soon as the rest of the party could meet the AoE requirements with the single-target mage alone, allowing the other caster to better aid their clear times between add burn phases. Because not every fight has equally weighed inclusion of AoE phases by which the mass-attack mage can play his part to make way for the rest consistently, this cannot be stable nor inclusive design.
3. I've not forgotten that BLM is highly dependent on consistent, immobile uptime. I've mentioned as much multiple times in the post you're quoting. Since you proposed that SMN's greater access to mobility was a point of concern to any attempt to balance the job, I suggested three approaches: increased turret-time dependence for SMN, increased mobility (as per your earlier suggestion) on BLM, and increased potential output from SMN's current immobile casting in exchange for reduced burst AoE potential (thereby reducing the gap in maximum ST output--currently slightly BLM dominant, and by-event or burst AoE output--SMN dominant).
If you feel the need to respond to a part of a given post before you've had the time to read or digest all that's been said, but still feel like you need to suggest the context of the whole post, I'd recommend duplicating the tab, replying in one, and having the original in the other. You can split the screen to a half or so each or, if on Windows, alt-tab between browsers if you've split one off, or ctrl-tab between tabs if left on the same browser.