1. The new gTLDs come and go, and sometimes even change ownership, AFAIK.

2. The rules can change somewhat arbitrarily. Or the rules might not change, but their enforcement might.

3. The registries have no incentive to treat their TLD management as a stewardship of a public good; they are in it for the money, and might de-prioritize technical development and/or support to arbitrarily low levels.

Running 10 gTLDs is about as hard as running 1 TLD. You already have the nameservers and the servers that handle registering domains, etc. Most of the rest of the work is done by registrars.

Further, TLDs are bought and sold periodically. I haven't seen any gTLDs go away. Is that something you've seen?

Otherwise, the concerns listed seem like FUD with no evidence so far.