STRC is much riskier (I'm having trouble imagining any scenario where it does NOT default.)

STRC has only been around for less than a year. I don't know too much about what assets it holds (and maybe it's worth me looking into it), but those kinds of returns are generally a sign that you're taking on a lot more risk than you think (even if it hasn't had a major price decrease yet).

We're competing against long-term cash held in a money-market fund (an instrument optimized for short-term use with same-day liquidity) earning 3.5%. In that context our yields definitely are competitive.

I googled it. That is Strategy? Ponzi Saylor's company. Ooook.

Why not buy Celsius (1) instead, even better yields ;)

(1) https://en.wikipedia.org/wiki/Celsius_Network