Preventing the ISP from accessing the router is almost certainly a violation of the terms for most ISP'S so you do that at your own risk though certainly the safest method is using Virtual Private Network (VPN) to encrypt your internet traffic and add an extra layer of privacy.
No product is immune to issues or wear and tear. That is why Instruction manuals often include sections dedicated to troubleshooting common problems and providing maintenance tips. This proactive approach equips users with the knowledge to identify and address issues promptly, extending the lifespan of the product and minimizing disruptions to its functionality however there no such thing on the manual every user has different networks and there should be a specific guide to identify there networks if were going to talk about unknowledgeable individuals and not just plug and play.
I'd agree with you however if you paid a premium for product and you had to be the beta tester for it what does that make you?