Support Tier list 7.24 (Personal opinion)Support Tier list 7.24 (Personal opinion)Support Tier list Patch 7.24

1- Trundle is great against tank I'll give you that but as a support he doesn't offer that much CC or Peel and being a support his gold income are pretty low meaning building like a toplaner to deal damage won't really work. The only avatange he got is like you said that he is strong against tanks but that's about it, as a Support he doesn't deal that much damage, he isn't that tanky being lower level and having less gold income and he only got his Pillar to really peel for his ADC :/
2- Sejuani is an amazing tank because of her passive but she lacks synergy with ADC. She can only use her E with other melee champion and with the exception of Mordekaiser they is not that many Melee ADC making her the only source for her E. She got great CC overall with her Ult and Q and got a good slow with her W but she don't really bring anything special to the table. I'd say the only thing that she brings that other supports don't is her synergy with most junglers, her main strength as a support is probably that she can set up ganks easily with her Q and Junglers being mainly melee can easily help her with her E. But other then that she doesn't the thing that an Alistar or a Leona could do so yeah not the most unique Support but I believe she got potential if played right ^^
3- I believe Shen is great in a splitpush composition because of his global present with his ult but as a Support it can be really hard to have global present because well you're a Support not a Toplaner meaning, just like Trundle, he doesn't have an gold income big enough to build the way he would as a Toplaner. And being levels behind is ultimate will take time to get to that third level meaning that his global present is not that strong before late game. But he got great peel and engage with his taunt and W blocking Auto Attacks which are the main damage of ADC. His Q does good damage early so he is a good source of damage for early trade but where a Toplane Shen becomes a Monster of Splitpush in late game I believe Shen Support is the opposite, great in the early game, meh in mid game and kinda bad in the late game.

I hope this answers your questions and that you were able to understand it ^^

Lulu is that high for the same reasons that Janna is high: Her peel is amazing. Her ult and shield + her Polymorph that shutdown everything that tries to kill your ADC is great. And she got decent damage in the laning phase with her passive and Q wich can be really useful for early trades. Karma is kinda of a weird case, I believe that yes she is a bit high but she isn't bad enough to be in the Average Tier she kind of is in the middle. Her Q damage is great for early trades and waveclear and her Mantra E in late game can really turn the tides of a fight by buffing your team at the right time but what made Karma so strong so early into the season is that ADC didn't had tha many option to sustain her constant poke but now ADC got those option with Shields, 3 long swords or with Bloodlust so she lost one of her main strength meaning that she is no longer godtier but she isn't trash either. Like I said earlier she is in the middle of Great and Average so yeah. Alistar can clearly be in the Great Tier I 100% agree with you buuuut a trash or even an average Alistar cannot do that much, being a full all-in support like Leona he gets shut down pretty easily by Lulu, Janna, Soraka and other very heavy peel Supports to the point where he is almost useless against them. All the placemnt in my list are for average player, because If I was to make a tier list for good players well Thresh would always be Godtier because of how good he is if you're good with him. So I'll say you this: If it's a good player 1 Tier up if it's a trash player 1 rank below and well like I said if Average it's stays like this. I hope my english wasn't too bad for you and that you understand my point of view and remember, this is MY read in the meta for supports, I'm not a Godlike Support, I consider myself a good one but not the greatest I'm not SKT T1 Wolf or Aphromoo or Biofrost, I'm just a Supports Main who reads the current meta this way ^^'

I added them ^^ Sorry I don't speak portuguese ;x