The designers of cars have considerable problems when trying to set up the seating position for all shapes and sizes of drivers.
I'm not being sizist, but a car has to accommodate the tall and the short (I'm the latter) the slim (that's me again) and the increasing proportion of drivers who are overweight. If you are short in the leg (me) then you have the seat fairly well forward and possibly set higher than someone of more substantial girth.
So, opinions about how a car fits a driver are almost wholly dependent on the body dimensions of the driver. One size definitely doesn't fit all.
The relative positions of the seat, the armrest, the handbrake lever, the gear stick, the steering wheel and the pedals are all a compromise designed to fit the "average" occupant and with the best will in the world, will not please everyone.
Like the OP, I find the armrest doesn't move far enough forwards when I'm on a motorway, but when I'm driving on other roads I slide the armrest right back as I feel it gets in the way when I need to use the handbrake.
And no, I don't know of any way of extending the armrest forwards.