I think the point of hybrid is to reflect the real world where countries that use metric (ie all of them except 3) still have to use knots and feet and miles because those are global aviation standards. But you only see miles for distance and knots for speed in the avionics; in the sim UI you’ll see distances in km and speeds in km/h (personally I think that last one is a mistake; everyone talks about aircraft speed in knots so in the UI it should be displayed in knots or both).
Steam gauges are a problem here, because aircraft are usually designed based on a reference and that reference often has instruments using US units, including in some older aircraft speeds in mph rather than KIAS. Ideally the developers should offer a metric cockpit version with the gauges in the units they would be in for an aircraft flying outside the US. Steam gauge altimeters can’t always be changed to HPa, but the G1000/3000 has the ability to switch to alternate units, you just have to do it in-game. Some aircraft have the ability to switch between lbs and kgs for weight and fuel in their FMS, where they have one. In the UI itself for fuel and weight and balance you can always switch between lbs and kgs.
I agree that it’s frustrating and that you should be able to choose your own mixture of units. You cannot now. I suspect it’ll be low down the wishlist, though.