Due to them being true CCs though, while I captured the option premium on the day I sold it, I would lose that premium and then some buy buying back near expiry at this new, much higher price, right?

Yes. If you sold (to open) an option at $10 and now it is worth $20, and you want to buy (to close) it back, you pay $20 and have a short-term capital loss of $10.

IOW, now that the price has blown past the strike price, even though my actual shares are currently worth the going quotation, I'm not able to sell for 468.65 or whatever. I'm stuck selling for the CC strike.

Not completely true. If the option is exercised, and you are assigned (and this always happens in the money), then you have to deliver shares. But you DON'T HAVE TO deliver old shares held in your account, you can buy new shares and deliver them. Anyone who thinks about the process for a brief period would realize that this MUST be true.

Here's an example:
You hold 500 BRKB in your account, their basis is $50.
You sold 5 strike price 450 calls for $20 each.
The call is exercised and assigned to you. You need to deliver 500 shares, and you will be paid $450 for each of them.
You have two choices:
1. Deliver the long held shares in your account. You will sell them for $450, and I think your long-term capital gain will be $450 + $10 - $50 = $390. It's possible that the $10 option premium is a short-term gain, not sure. Someone please comment.
OR
2. Buy 500 new shares for $471 each and deliver THOSE shares. You will incur a short-term capital loss of $450 + $10 - $471, or a $11 loss.