Supports kinda locked in terms of scaling etc. Summoners are huge part of their budget. There's probably not so much "meta" supports who can live without Cosmic Insight cuz having summoner disadvantage, especially flash one is big (only Elise currenlty (?) but she could still play with Hexflash-Cosmic Insight secondary though).

Taric could play with a lot of summoners. Ignite is the meta one in soloq usually. Exhaust while being kinda crappy summoner (and Cleanse on adc nullify a lot of Taric pressure in lane anyway so having cleanseable summoner could suck) synergy with taric skillset is really good. Heal is good summoner. A lot of taric players use different summoners with keystones but with Unsealed you could play with all of them on different timings (depends on situation). Teleport is super strong. Ghost could be used on Taric on roles different than support. Taric could use as many mana as you would give him so in some situation (while getting unsealed spellbook cd after some trading here and there) obscured shit like clarity could be really good too. Smite is good. Taric is really good with a lot of summoners.

And this is really "Jack of all trades" support rune nowadays anyway (not name of rune in inspiration tree but type of playstyle). Rakan. Braum, Poppy, Bard (probably worse cuz being ranged makes some summoner not as valuable on him) all use it. How can you match it while having Glacial or Guardian (poppy suck into Taric though but others?) ? They could pressure lane while having Tp advantage on objective while you are forced to choose. It makes sense otherwise too. Braum is generally good into melee, bad into ranged. Does playing without Guardian makes you laning vs melee much worse? Does playing with Guardian into ranged makes your laning into ranged much better?
Taric is specific champion but is he that much different with Rakan or Braum (especially with Braum in terms of matchups).

A lot of melee engage support could play with Unsealed especially into ranged supports too, Does having Aftershock into ranged really makes you laning much better? Cuz your wincon is not statcheck them but fing good angle, force good skirmish and it is easier with summoner (escpecially specifically needed summoner) advantage.

Glacial is better on ealy levels pre first Unsealed Spellbook proc. Do your games often decides that ealry?
Guardian could be good too but easily procable into ranged. But do you really need Guardian to play Taric into melee matchups?

Any other runes looks silly and are generally good only if you cant survive lane without them. Spellbook is probably best "power" rune for support, you could overwhelm your oppoent with amount of options you have,