I see it more as "convention over configuration". If you want to (or need to) tweak the configuration and settings extensively, then that tool is perhaps not for you, and that's ok. Perhaps you are a subject matter expert, and you want more control.
If you're ok with sane defaults (that were chosen by subject matter experts, and you are not one), then "opinionated" is a great thing.
Whether it impacts a specific use case is usually here nor there - itβs usually about maintainability. And while finding contributors for open source projects can be difficult, finding people who want to do the thankless work of maintaining code long-term is much harder.
That's one way of looking at it. Another way of looking at it is to emphasize minimalism, the UNIX philosophy, and keeping maintenance burdens low. Sometimes, neither is the case - Ruby on Rails being the classic example of an opinionated framework, one that did expand to add additional functionality over time.
Wireguard is not opinionated, it just has a very limited scope. It has one job, to create an encrypted tunnel between two endpoints, and leaves literally everything else up to other tools to build higher-level functionality upon. Contrast with OpenVPN which requires you to be your own TLS certificate authority and all the complication that goes along with that.