LLM's are not useful enough to me to want them integrated with my daily-drivers (web browser, email client, etc.) - so this is a great take & one that I personally identify with.
If every company and their dog started churning out their own LLM as a business or revenue model, one can easily see the supply overwhelming demand here apart from many other problems.
This certainly seems the case on the iOS/Play stores. Primary AI apps from the big hitters (OpenAI/Gemini/Copilot etc.) but then loads of knock-off ones from those riding the AI hype train. All the knockoffs being basically wrappers around APIs from the big hitters with ads/in-app purchases.
As a dyed in the wool Firefox user, I am of course very used to disappointment about how they direct their development effort. There are a million things I'd rather see them work on than strapping in an LLM. I don't know much about the Vivaldi community but I assume they took this into account when making this decision.
You don't have to cater to every user. Focusing on things you do better for a huge portion of potential users is a much better decision. If features turn out to be so useful that everyone needs to integrate them to not be left behind you have to do it. LLMs are not there yet. They are to unreliable, expensive and difficult to run locally. In a few years when most users might be able to run decent models locally you can reevaluate that decision