I have a 165 mm santoku as well as a 165 mm nakiri. I find myself using them both, sometimes in preference to a 210 mm gyuto.
The santoku is nimble, lighter than the gyuto, and shorter. If I'm making a meal for just myself, with small amounts to be cut, the santoku is nice. That one knife does everything for the whole meal, especially if there isn't any slicing of meat or fish, where I'd reach for a longer blade.
The nakiri is great when I'm making a big pot of minestrone or some such. Loads of veggies to be cut. Hard to beat for that, and I can wave it around with abandon without banging into things and damaging the tip. It's compact, tight, fast, robust, and pragmatic. I don't have to watch every move I make when using it.
Still the gyuto rules for me. If I had only one knife, that would be the one. But, like any other all-purpose tool, it makes compromises, too. (Universal spanners, anyone?)