There is some key info that must be missing about your previous installation. Companies don't typically mix and match install types unless there is a compelling reason.

As far as the mulls, if you do a full tear out those will be vinyl, yes. That is unless you actaully build new mulls in the hole and install separate windows. If you do pockets, mulls are often removed in that case as well, although they typically can stay if you prefer.

Issue here is that you have conflicting goals. On one hand you don't like the idea of vinyl mulls, but if you leave wood mulls in, the windows/glass will be reduced that much more which you stated is also an issue for you.

I don't think that your pic of windows over a sink is the best point of reference for this. That opening is fairly small for a triple unit making the frames more pronounced. It also looks like it may have been measured small and there is some extender trim creating a "mass of whiteness" the likes of which would be found at a Bon Jovi concert.

Actually, I have found other images of this triple kitchen window elsewhere on line., like the one I included here. It makes me think, it might just be how the OKNA makes them. Until mine showed up, it never occurred to me in a million years that it would look like that. I have seen lots of triple windows, and had never seen one so aggressive around the dividers. The Andersen window was a triple there too, and it was far more svelte. As I researched windows since I got mine, I found triple windows are not usually on display anywhere, nor are the bay/bow windows. You’re stuck trying to imagine what they will look like from a brochure. I would advise people to work with someone local, so they can direct you to a gallery of their work examples. Still, you might not be able to see what the windows look like from the inside….which would be important.🥺

This one here would have been more along the lines I was looking for. My guess is it’s wooden one though. 🤔 Surely, there are vinyl window brands that have more slender dividers than mine.

Basically any window, except for wood, will be based on 3 frames mulled together. This is the norm.

I'd agree with the comments above that the window being on the smaller side for a triple makes the mulls seem more pronounced. The Okna casement is one of the more narrow lined vinyl windows on the market (more glass), and as WoW alluded to, they simply mull one frame directly to the next.

Are there windows of other materials with slightly more glass? Certainly. The depth of a mull cap compared to the flat surface of a zero mull vinyl unit can play tricks on the eye as well.

As far as full frame vs insert, and mulls in or out, there are certainly tradeoff's.