Complicated kitten!

Hi everyone I'm Mint and I have 5 month old kitten who is giving me the hardest time with food.
He is up to date on every shot, and is neutered.
I have talked to my vet but they are not giving me many solutions. They advised me to try hills but I refuse to feed him that.

When I first got him he was on fancy feast and hills science diet. I switched him slowly to wellness core kitten dry and jumped right into giving him wellness core kitten wet, BB wilderness kitten wet, and nutro natural choice kitten loaf.

He never ate the dry food since the kibbles were too big so I switched him to Merricks kitten dry and he's been eating it just fine. He did have black stool for a while but after a stool sample the vet said it was due to a diet chance.

It was my mistake to give him so much variety of wet food but my previous kittens did fine with the variety. I cut it down to just giving him the merricks dry and bb wilderness kitten. 

In the last two weeks he's had massive stinky diarrhea with some mucous blood and after two stool samples he is showing no signs of parasites. The vet advised me to keep giving him the medication to treat giardia for 7 days. 
Two days ago, I cut out the BB wet food and strictly fed him merricks (I even wet the food down to make it resemble we food) and his stool is more solid and doesn't stink anymore. I honestly think it was the blue buffalo can food causing him the loose stool.

I started to give him Natures Variety chicken wet food along with the merricks today and he's having more formed stool.
My question is....should I
A. cut out the dry and only feed him wet?

B switch the merricks to natures variety raw boost?

C switch him to natures variety raw food?

I don't know what to do. I keep hearing that dry is so bad and I don't want to be a bad kitty mom. I just want my baby to get the best nutrition his body will tolerate. 

Being a kitten with a sensitive stomach I don't know what I should do. I don't give him ANY treats in fear he will have diahrea. I watch him poop like a hawk....It's so sad.
 

All wet food is best but at a certain age I find it hard (and expensive!) to keep up with their caloric needs with just wet food. So older kittens get some kibble. If you don't mind the cost and frequent feedings (a 7-or-8-month-old male may be eating 10+ ounces a day!), switching to all wet would be great. Switching to NV raw would also be good, again, provided you don't mind the cost. I don't know if switching to NV Raw Boost kibble for his dry portion would be better for him or not, I guess that would depend on his tummy.

I've heard not-great things about Blue Buffalo, it seems like a lot of cats can't handle it. Maybe Wellness or Nutro would be easier on his tummy. A probiotic and/or enzyme supplement may help too.

Thanks Willowy for the response! 
The only issue I have with all wet is he isn't on a schedule for the dry so he has it all day so sometimes he'll nibble at the wet and then come back to it later. I only give him a 3oz can of wet a day and 1/2 cup dry which sometimes he doesn't finish. I just want him to put on weight.
I don't care about cost but I do care about wasting food if he doesn't eat it or if it goes bad from being outside too long.

How about doing a mix of all three? Wet dry and raw? Or should I wait till he gets older to cut out the dry? I'm so flustered. I don't know what to do. 

I am going to buy him a probiotic for sure tomorrow, I've been thinking of it for a while. How about missing link supplement?

Is there a better brand of wet/dry food sold at petco?