Nope
Doesn't work like that, if you could get free focal length everyone would be using teleconverters instead of buying a separate scope for each FL.
Like I said probably won't really notice a difference in daytime photography. But you will lose stops and image quality with ANY teleconverter period. Is it noticeable for daytime photography? Probably not. But there is a difference
But at night with the most demanding subset of photography - night star fields and objects you bet it does.
There's no way you are convincing me that there is no IQ difference when you slap a TC on a modern camera lens from any nikon or canon.
Well, it doesn’t matter if you are convinced or not. 1.4x teleconverters for mirrorless are so good now that Nikon literally builds them
into their supertelephotos. You can’t remove them, just flick them into or out of the light path. Olympus has a lens like that too, and Canon started the trend in still photography IIRC with their old EF 200-400mm f4 (which wasn’t as good as the modern mirrorless versions).
Of course there has to be some small loss of quality and one stop of light. Realize because these built-in teleconverters can be tuned exactly for those
individual lenses vs the older general purpose teleconverters that needed to work with many focal lengths, lenses, and f-stops. Any quality loss from these new built-in TCs, especially, are invisible in today’s normal photography.
Nikon SLR teleconverters for the F-mount were never as good as Canon SLR EF mount versions (esp their 2x). Maybe this is where you’re getting your bias?
Now the answer to the question if the optical quality is up to snuff for your
very specialized area…that is beyond my expertise. But the mirrorless teleconverter quality at this point (even the separate mirrorless TCs) is good enough for pro nature and sports photographers, believe me.
Top end bird photographers, in particular, are picky as hell about feather detail. Like, crazy picky. But they’re not shooting geometrically near-perfect balls of light like you lol.