Because Astro was initially terrible, then incredibly overpowered? We're talking about a period with some of the worst healer balance in this game's history. Which is saying something since healer balance has always been a crapshoot. Naturally, you're going to see a lot of complaints in general.
Few, if any, of those topics had to do with AST's speed ranking and more to do with how grossly imbalanced it was throughout HW.
You're misunderstanding. White Mage wasn't the best healer in terms of heals. It was simply better than Astro in 3.2 despite several buffs the latter received.
They overbuffed Astro because so few players were willing to give it a second chance. It was literally them begging people to play it. Had they night made such a desperate decision, Astro would have gone an entirely expansion as effectively being worthless. Considering it was a new job, they wanted it to at least finish strong.
Actually, no. Astro was underpowered until 5.1. From that point onward, it is generally viewed as having the much better healing kit due to its sheer abundance of oGCDs. White Mage leans more towards being the DPS healer.
Which didn't work. Partly because, at the time, FFlogs ranked based on pDPS. Since people care about their percentages, Astro was always preferred. Had their ranking system not changed to rDPS, White Mage would continue to live in Astro's shadow.
What do you purpose they change it to? Of the six cards, five would be worthless nowadays. Even if they split Royal Road to have an offensive and defensive card slot so Bole no longer competes with Balance. The devs still need a system where Balance, Spear and Arrow aren't just "Damage, less damage and even less damage."
Unfortunately, this game lacks in the way of interesting gameplay when it comes to numbers. Bard used to interact with Crit, however they removed all that due to its immense power creep. Haste buffs, as noted in my previous post, cause a myriad of issues with far too many jobs. This doesn't exactly leave many options for card expression without fundamental design changes.