Not sure what would've been the riskier bet. Coinbase of course could have pivoted away from Bitcoin if it didn't work out. But there are plenty of scenarios where Bitcoin succeeded, but this startup didn't. Pretty interesting that Coinbase wasn't an any more interesting investment than Bitcoin at the very start, and that while Coinbase was private, hard to invest in, and illiquid if you held it, Bitcoin was open to all to make the same bet.
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Also find it interesting that the real bet that Brian made here in his post, on building a product to undercut CC fees, didn't really materialize. Coinbase invested heavily into this, building out a marketplace for merchants for payment processing. But virtually all money is being made on being a broker for people speculating on Bitcoin as if they're buying gold, with no significant intent to use bitcoin. And payment processing is still 99.99% non-crypto, with crypto-based payment processing still being slower, costlier and less trusty.
If you got me in 2012 in a time-machine to 2021 to only take a peek at the current virtually-zero level of actual use of Bitcoin, and the abundant alternative non-crypto digital banking/financial products available, and asked me to invest in Bitcoin or Coinbase... I'd have said no. (I was optimistic, so I did invest back then). I wouldn't have predicted the current price levels even with information of today.