You can use them to level up soldiers of other classes in Academy. It must not be 3 soldiers of the same class - but there is a risk involved (you get one of the soldiers back randomly). Or there are some “Academy orders” from battlepass that allow you to choose what soldier you want back.
This is exactly how I use tankers, especially because they level up very fast.
Well, that is what we get with RNG mechanics. Before OBT there was at least an option to “send them” to rear, so they would not fill the reserve.
For getting exactly what you want there are silver orders, so I doubt that they will split bronze order even more.
Oh, right - i missed it somehow. Are you sure that is only for premium account? Because that would make it even more frustrating and should be changed immediately.
I did some testing in that matter and noticed that if you have only 20 or less soldiers in reserve then you can’t send them back to rear anymore (even with premium account). So there are some wierd things going out here.