What was Bitcoin "promised to be"?  How does the Bitcoin of today not fulfil the description from the Satoshi white paper?  Bitcoin is more useful than Monero because it does not force privacy upon its users.  It gives its users the freedom to choose their privacy requirements.  Cryddit (Ray Dillinger) made a series of insightful posts beginning here arguing against all but niche adoption of strong-privacy coins.

Furthermore, even if you assume that protocol-enforced privacy is a positive (which I don't), the trade-offs made to get that privacy have real costs.  But we won't fully know what these costs are until something like Monero is trading at a much higher market cap and transaction volume. 

That being said, I like Monero because (a) it had a fair launch, and (b) it offers something unique.  I would love to see it overtake Dash (Darkcoin) and then Litecoin.  But I think best-case scenario for Monero is a few % of the bitcoin market cap.