You sound like you should be taking biological drugs. The stricture at the J Pouch inlet should have been dilated, did they do that? I am strictured in the same area- J Pouch inlet- it is very common due to backsplash stool and resulting SIBO. My Doc said he would only dilate me if he couldn't get a scope through. He has always been able to. If that is the specific source of the blockages (which is not clear from your post), dilation would rectify the issue, although there are some risks with that.
You have not provided enough information on what antibiotics were attempted other than flagyl. Although flagyl is one of the key ones, there are around 6 or 7 others that I used to treat pouchitis effectively for almost 25 years. I am on Remicade now, have had the J Pouch 28.5 years and my quality of life is very good.
An end ileostomy could be a solution, but frankly there is not enough information in your post about whether you have exhausted the two lines of treatment which are antibiotics and biologics. It's possible if you have effective treatment you can keep the pouch, although that may mean frequent or continuous antibiotic treatment (other than flagyl with drugs like cipro, xifaxin, augmentin and keflex) or with biologics like Remicade, Entyvio, Stelara or one of the other biologic drugs. I would not give up on the J Pouch yet. I would also seek a doctor experienced with treating problematic J Pouches. Good luck.