CrossCountry going back to an hourly service will be a vast improvement, the sooner the better. They also have a fleet refurbishment plan including the Stansted Class 170 fleet. I agree is has little value much beyond Peterborough but is a valuable link up till then.
Stansted to Peterborough at half-hourly isn't currently achievable due to platform capacity at Stansted and bottlenecks in and around Ely. None of that will change probably for at least the next decade.
With regards to Greater Anglia from Norwich, these are replaced by additional Ely - London Liverpool St runs at peak times. The Stansted extension south of Cambridge on the hourly Norwich - Cambridge runs unfortunately can't co-exist with the additional Ely trains running south.
There is talk of Norwich - Cambridge going half hourly but that again couldn't go all the way to Stansted. The single track tunnel beneath the Stansted runway according to GA allows only six trains each in and out per hour, which is already being hit (4 StanEx, 1 GA and 1 XC).
I personally would rather the hourly Norwich - Cambridge be extended to Stansted Airport all-day in place of the extra Ely - Liverpool St runs, given commuter traffic is below 2019 levels whilst airport passengers are exceeding. Plus Stansted Express and the newer Class 720's on commuter routes provide plentiful peak time capacity along the West Anglia line and provide more seats compared to the older trains they replaced.