Second, IOTA was not designed to be a currency. It was designed for secure machine-to-machine communication for the IoT industry, and has several real world usages already in the works which will take over technology that was originally considering blockchains.  Byteball's only purpose is to be cryptocurrency, and has no other reason to be used or developed further or used by any enterprise businesses for any other purpose.  

The Proof of Work (PoW) is simple, and it is to avoid Sybil and Spam attacks. It doesn't create tokens or anything, it just validates transactions, and doesn't get more difficult over time, its a fixed difficulty. Its nowhere near the same thing as Bitcoins proof of work and artificial difficulty adjustments. On top of that, the proof of work can even be outsourced from small lightweight devices to something more able to handle the computational load.

The coordinator is going to be turned off very soon actually. It was said to be turned off this July. I understand fully why it was needed.  The tangle had to grow beyond a certain point to prevent a 34% attack.  You can read more about it here: https://forum.iota.org/t/iota-double-spending-masterclass/1311  There are only so many ways to get a DAG off the ground, a coordinator is one way. But once it is flying, it will soar.

Byteball didn't solve any problems really, they just shot themselves in the foot with transaction fees, and removed some security...