A good point but each train has around 20 seats which are not reservable - a few of which have extra legroom. Just look at the seat map for NR and it will tell you where they are. You will never be turfed out and the lack of information screen above the seats confuses people so they avoid them. And you can quite confidently say "no I'm not" when someone claims you are sitting in their seat!
I did have to stand once between BHX and BRS but that's because I elected to take a quicker train whereas of normally get the direct one.
Yes its busy particularly between York and Leeds but I'd rather that than FAFF about changing.