Bitcoin itself has proven PoW a failure.
Well I'd not go that far, it's seems to be working, but with flaws and serious limitations, and a huuuge waste of energy.
Anyway, I'm still fond of PoS like you, but in general blockchains are limited (scalability, growth of the chain, fees).
The way IOTA uses PoW is totally different, because there are no blocks and you only need to do very little PoW when doing a tx, so no energy gets "wasted", and the network is already proven to handle 30+ tps without any fees (100 tps are possible right now).
Working , but ignoring the fact China completely controls it, just like the yuan.
If IOTA uses PoW, then it still has all of the weaknesses,
1. PoW mining will be out of the reach of all but the ultra rich.
2. The coin itself is completely useless without the work provided by PoW device, which draws excessive energy and requires constant updating to stay competitive.
ASICS Arms Race
Proof of Stake the value is directly in the coin , not the PC it resides on,
As far as TPS, that is really a non issue that can easily be solved with off-chain transactions.
Example: Gift Card System
(Allows Unlimited Transactions Off-Chain)A Gas company can issue me a card , I send them
ZEIT to fund the card,
(This Transactions is on-chain and recorded in the blockchain)they record the balance and credit my gas card with that amount.
When I buy the gas with their card , it deducts the amount of
ZEIT from my balance,
and issues me a receipt from their record keeping system.
(This Transaction is Off-Chain and not recorded in the blockchain , only on their internal record keeping system.)(Meaning there is now No Limits to Off-Chain Transactions) 
