How exactly is diploanexation OP?

[DDRJake]

If you expand your Sphere of Influence massively which is very cheap and easy to do if you are already large, you get an absolutely massive bonus to your diplomacy skill and can quite easilly diplo-vassalise most 3-or-fewer province countries. Using this you can pretty much diplomatically conquer the HRE provided you are already fairly strong yourself.

Some people are fine with that, others want the extra challenge. Live and let live.

 

[DDRJake]

Not 4 countries in your sphere of influence, more like 20 or 30.

 

[DDRJake]

Still diploannexed my 26 province Byzantium vassal a week ago.....
Your argument has been rendered invalid.

You can diploannex a country of any size. I diploannexed a 52 province Brittany once, my chance was "likely"

But you most certainly did not diplovassalise a 26 province Byzantium.