I'm also still wrapping my head around this just like you, but I think I understand enough to answer some of your questions.

> We know transactions are slow and expensive, so it’s not a good replacement for ordinary commerce.

I don't think that this is obviously true. Digital transfer of the US Dollar is similarly slow and expensive (see: ACH, Wire, SWIFT). The response you'll hear the most frequently is that BTC (and digital currencies) should be compared to the US Dollar, not to Visa and Stripe and Venmo etc. Right now, if you want to send US dollars to somebody and you're unable to do it through PayPal/Venmo/Square/Visa/MasterCard, your best bet is to literally mail cash to the recipient. BTC solves that problem; you now have the option to send someone "cash" in a trust-less way, but that's probably not how the majority of people would use BTC.

The blockchain doesn't have to be used to settle every single transaction in real-time, just like you don't have to use ACH/Wire to send $5 to someone electronically for every transaction. Just like banks today send a batched ACH files of all money movement at the end of the day, they may do the same on the blockchain hourly/daily. The benefit of BTC over USD is that there is a way to "mail someone a briefcase of cash" without having to actually mail them; instead you can "mail" it to them on the blockchain and have it take a few hours rather than 3-5 business days. If you want to send US dollars faster, you can rely on centralized institutions that build financial products on top of the US Dollar, but the same can happen on top of other non-government-backed currencies. Just like you have a bank account where you can see in Dollars or Yen or Pounds what your bank balance is, one ought to be able to open an account and see what their balance is in BTC or ETH or Nano...or so the argument goes.

> It also lacks a lot of the controls that traditional banks have for good reasons, so fraud becomes harder to tackle, and things like refunds are just at the mercy of the other side of the transaction (making commerce even harder, as well as basic banking)

Again, you want to compare BTC/ETH to the actual currencies, rather than the institutions that engage with those currencies. All of what you said is true of any fiat currency: I can physically hand you a $20 bill, and that transaction can happen in a totally un-traceable way already. There’s a common saying that if cash were invented today, it would be illegal, since it’s hard for the government to track and they wouldn’t like it.

> So then it becomes a digital store of value, one that is only as valued as the market gives it, and typically markets eventually correct when there’s no underlying true value proposition (as we can see with $GME).

This is a good point, but I found a good "counter-point" in Matt Levine's latest Bloomberg Money blog post: https://www.bloomberg.com/opinion/articles/2021-02-16/goldma...

Here is the relevant bit:

"We have talked a lot recently about the Reddit-fueled rally in meme stocks like GameStop Corp. One thing I have said about this rally is that it reflected Reddit traders’ correct understanding of a simple market dynamic, which is that if they all bought the same stock at once then it would go up. So they did. Institutional Bitcoin adoption, as we have also discussed, has a somewhat similar dynamic: Each time a big institution says “we like Bitcoin now,” Bitcoin goes up, because widespread mainstream institutional adoption is clearly bullish for Bitcoin at this point. So if you are a big institution or corporation, you can make some free money by (1) buying Bitcoin, (2) announcing “we like Bitcoin now,” (3) watching Bitcoin go up, and (4) selling the Bitcoins you bought for a quick profit. (Or keep them as a bet that other institutions will do the same thing and you’ll make even more profits.)

This dynamic, separate from any particular institutional decision, is good for Bitcoin: If it’s in every big bank’s and corporation’s short-term financial interest to quietly buy some Bitcoins and then noisily make a show of adopting Bitcoin, then a lot of them will, which will have the effect of pushing up the price (both because of their buying and because of their announcements). Unlike meme stocks, there is no underlying business, no cash flows that do or don’t make the price make sense: The price of Bitcoin makes sense or not purely as a social fact; if there are “fundamentals,” they are things like “widespread mainstream adoption,” which you can provide. “The fundamentals of Bitcoin are strong, look, Morgan Stanley is buying some,” Morgan Stanley could plausibly say, after buying some Bitcoins. So it might as well do that.

With the meme stocks the natural thing was to worry about the endgame for that process; you can’t have a stock price that is divorced from fundamental value forever. With Bitcoin, you ... can? Like if the endgame for Bitcoin was “universal adoption by corporations and institutions as a digital store of value,” then that sounds like a good and permanent and somehow fundamental result?"

> so it’s terrible as a wide spread value store because it removes an important tool that governments have to handle the economy (dealt with debt via inflation aka printing money, which can be executed “well” (US) and really poorly (Zimbabwe)).

This is very debatable, and you've more or less illustrated the controversy by pointing to a "good" version and a "bad" version. The political question is whether the possibility of "bad" means that the concept of government-controlled inflationary assets is inherently bad. I won't pretend that there's an objective answer, but neither should you; the fact that it removes the tool you describe can both be described as a feature or a bug, depending on your political leaning.