Meiling isn't a pure tank yeah, but a bruiser kind of thing is definitely what she is. Imo, Meiling is a very good at her role. Passive defensive buff, damage reduction 2nd slot, ability to heal and cleric other people while being able to do moderate damage, and if you give her warrior subclass her damage actually becomes quite good. An example would be Meiling doing about 20k ish damage to Ama no Murakumo at 12% atk and Ama no Murakumo has no buffs/debuffs at all. Meanwhile, an 80% atk Kasen with level 3 Higekiri's cursed arm dealing about 60-70k damage to a non buffed sword. For a move that's not super effective, I would say that's a good amount of damage.
I would say Meiling is best 2nd slot tank, in all honesty. I never made Meiling into a pure support (like healer) but from what I heard healer Meiling is very good. Literally never die.
Sometimes when I use Meiling I feel like she's too fast. Her Brilliant Light Gem putting her gauge at 80% really makes her "fast". It messes up the timing on some of my shenanigans.
To compare Rinnosuke to Meiling is kind of weird to me, cause Rinnosuke can be a very tanky attacker while being in the "FIRST" slot. Meanwhile, Meiling's sole purpose is to be a 2nd slot tank. So maybe you could go double tanky attacker Rinnosuke/Meiling in the first two slots, seems like a really cool idea, I should try that. But... I don't wanna get rid of my herbalist Komachi.