It's a hard one. I feel the UK were wrong to leave but Norway and Switzerland have a fantastic overall quality of life without and I'm not sure the benefits of membership unless you are financially poor country. Iceland is probably better off joining the Schengen but not EU.
Secondly, the world got a lot more unstable since the US is pushing for a lawless might-makes-right world and taking an increasingly predatory posture there. From that perspective, the EU is becoming even more relevant. Poignant example is Canada taking more and more steps to integrate their economy with the EU, as well as to become part of its security architecture.
UPDATE: Leaving the Horizon program has apparently been too painful [1], seems the Swiss were retroactively allowed back from 2025 [2]. I don't know about Horizon 2028 though.
1. https://sifted.eu/articles/switzerland-startup-talent-brain-...
2. https://research-and-innovation.ec.europa.eu/strategy/strate...