Update on my game, previously I had tripled in size by attacking Trebizond, Cyprus, and Venice and Rhodes defecting.
I beat the Ottomans single handedly and took back all my cores. No allies joined and my only vassal was Athens. Ottomans were joined by Crimea and Algiers. I didn't have to take any loans, although my treasury dropped from 250 to 50 and I had to fire two of my advisors.
It was hard (I nearly lost my fleet) and it took some luck (Mamlukes DoW'd Ottomans just as I finished occupying their European provinces), but I certainly don't think Byzantium needs any kind of buff.
Honestly I would be happy if rebels would stop defecting to Byzantium so easily, it takes a lot of the challenge out of it when you suddenly get super-rich Cyprus defecting to you with a free 12k army -.-