ASTs kit was set up in such a way that you didn't need bole for mitigation in raid content, they had enough baked in mitigation, same with ewer it wasn't necessary if you were good.
Spear, Balance and arrow were all dps gains. The only job arrow majorly threw off was mch and that could be adjusted around if you noticed you had the buff, and this adds to what i was talking about earlier about balancing around the averages.
You weren't only fishing for expanded balance in normal play, you were fishing for expanded (damage buff) be that spear, balance or arrow which you had a very high chance of getting, sure balance was better but not all that much better than crit, and if arrow had been adjusted that could have been another desirable counterpart. Bole and Ewer and Spire weren't their core healer kit, using them for their play effects were an added bonus if you got them, not core to their kit, they were designed for burning and rng manipulation. The only way a good rng class works is by having a less desirable option that can turn up, and if the player adjusts around it they still get a gain out of it, just not a large one. Balance was was massively overhyped in SB as fflogs ranked off of DPS not RDPS, going for the damage buff every min approach would be a pretty desirable effect this expac. I aggree arrow was a tad weak, but they could have turned it into a dhit buff.
You're placing way too much emphasis on some parts of the kit and being overly reductive about others. Basically every card was useful before just to differing degrees, spire/ewer were royal road fodder, balance spear and arrow were damage buffs and bole could be adjusted around if you got it, but really was the most useless out of the pack.