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Everything is a compromise. This optical design manages to be f/2.5 most probably because it does nothing to correct the plenty of aberration and defects it produces. Also f-numbers are deceptive regarding brightness and we should see how much light actually comes out from the other side, i.e. calculating its t-stops.

Also, a manual 165mm lens on full frame? I'm sure it could be great for interesting portraits, but street photography?

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Once you stop caring about image quality, the f-stop of a lens is only fundamentally constrained by the physical diameter and diopter of the lens. I suspect the f/2.5 figure is only being held back by the size of the lens barrel and aperture mechanism.

If it were actually well-corrected and apochromatic, then a 165mm f/2.5 lens would be fantastic for astrophotography. There's a reason the manual-focus Rokinon 135mm f/2 lens is so popular for that purpose.

And there is a reason why theanual focus Nikon 200 f/2 is, used, at over 2k Euro. Good professional lenses are expensive for a reason. Ehich is the reason why I stick to used ones for DSLRs, those are finally getting cheaper and easily available on the used market now that a lot of people switch to mirrorless and dedicated mirrorless lenses are covering more and more focal length and zoom ranges.

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