I understand your reasoning, and you are not wrong. There are a few problems with these abilities, in my opinion.
0 - This is only a small correction on your reasoning, it is a 2 minutes CD (at least) and not 1.5:
Blessing of the Summer (30 secs CD);
Blessing of the Autumn (30 secs CD, and need to be pressed right away to keep the 2 minutes CD);
Blessing of the Winter (30 secs CD, and need to be pressed right away to keep the 2 minutes CD);
Blessing of the Spring (30 secs CD, and need to be pressed right away to keep the 2 minutes CD).
And then you can use Blessing of the Summer again after at least 2 minutes. But, even for someone who doesn’t want to min/max the usage of the Blessings just to keep the CD in 2 minutes is just terrible gameplay.
1 - You are not wrong, a lot of those buffs are strong, even winter if properly used. But, usually, you ganna decided at the start of the DG who going to get the buffs and you gonna buff only those same people with the same buffs which are only boring. Right now I am thinking in something like (these examples were built with BFA experience so far, I am not taking SL changes in consideration):
Blessing of the Summer - Demon Hunters, Rogues, Monks or Warriors, the chosen one will be that can do more AoE (hits done, not damage) or have more haste;
Blessing of the Autumn - High damage classes (e.g., Fire mages);
Blessing of the Winter - Depends on the necessity, for damage or just get rid of it I would use on the same classes as Blessing of Summer or, during necrotic weeks, those who can do more AoE regardless of the damage done;
Blessing of the Spring - Tank, and someone who taking a specific mechanics.
2 - We have to keep tracking way too many things to it work properly (holy paladin point of view). Among our own CDs, we have to track each possible damage CD of our allies and the pacing of the dungeon (so we can use the proper blessings in the proper pulls).
3 - Terrible for pugs. In pugs you usually don’t know the people, you don’t know how they play. Now think about the previous argument on this scenario.
4 - Worst case scenario, you WILL use the buff on CD, which is just boring.
I love the idea of a buffer and I was struggling with how to make it work better than Divine Toll. Now I just gave up, (Divine Tool + Shock barrier (legendary) + Glimmer build) seems way stronger right now.
And right now I put myself in a situation as I predicted in the past to my friends, I will have to play as a Kiryan just because of their class skill, knowing that I hate every single thing about them and I love night fae the most. You can ask why, the answer is “If you are not on that covenant, we don’t have a spot for you”.
I hope I am wrong.