Just want to address the OP's list directly here:
1. Warcaster feat. Reaction casting to buff allies.
I am fairly certain this change is deliberate, and I'm not entirely sure why it's considered OP. How is using your reaction to cast
cure wounds on an ally more OP than using your reaction to cast
inflict wounds on an enemy?
2. Grappler feat
Lots of potential builds mostly abusing spike growth and spirit guardians. Basic idea drag opponents through spike growth edge or run around with a cleric and have multiple characters do it.
Personally I wouldn't allow someone to drag another creature through something like
spike growth without going through it themselves. The word "drag" implies that you are pulling the person behind you, not pushing/pulling them along bside you.
The changes to
spirit guardians are more concerning to me. I have discussed them previously. I'm inclined to rule that the spell can only affect each enemy once per round.
3. Conjure Minor Elemental. Not 100% sure it's fine at 7 but from 9+ there's some crazy numbers.
Yeah, this one is a problem and needs to be fixed, but as I said above, I think WotC has put it in their "wait and see if it's actually a problem at the table or not" basket.
4. Some sort of Monk weapon mastery abuse with daggers and unarmed strikes. Still work in progress. Looks like more damage than the -5/+10 feats without the -5 part.
I don't think know that this is necessarily OP either.
5. Some sort of turn yourself into a Kraken build. Work in progress.
I haven't heard of this one before! Can you elaborate?
6. Level 10 cleric abuse with spells like hallow.
This one definitely needs some clarification.