When I say I hope he gets more than a year, I say that in the knowledge that from next year, Yamaha are (supposedly) going to be ditching their inline 4 engine philosophy for a V4 configuration. This is a seismic shift for them from how ever many years of how they've done it.
A change like this may take more than a year to bear fruit and you need guys like Miller who have extensive experience riding this type of bike to propel the development. Who knows, maybe it does only take them a year to nail it in which case they can then look at a young upstart to pick up the reigns.
Additionally, Pramac are not a feeder team to a bigger marque (like VCARB is to Red Bull) so they have their own ambitions and aspirations and they will need all the technical nous they can get in this first crucial year or two.
In 2027, when the new regs kick in and things more less start back at 0 for all teams, hopefully the work Jack and Miguel have done will stand them in good stead.