That's actually the best course of action to do when you're waiting to get BTC in a lower price and try to DCA as fast as you can before the price bounce back up a few hundred dollars or a grand.
There a bit difference between holding a fiat and a stable coin thought they ultimately have similar value all the time, but fiat can't buy Bitcoin or any altcoin right away when you see a good entry point. With crypto's high volatility, it is possible to miss a good dip when you got a fiat converted into Btc or stablecoin.
And one last thing, I agree to both of you that keeping/saving a fiat won't save you even a few cents in the next coming years. I'd also suggest to buy properties and invest into real estate, it's safer than all of the investments in the market today. But if your risk appetite is in a tremendous level, then better invest in Bitcoin as well.
Honestly I would not put that much on stablecoins, 45% seems a lot. I try to keep it as "income" and that's much better for me. That way I know when to invest and when to wait, and my income makes sure that I could invest a lot more if I want to, and not invest if I do not want to, makes a lot more sense.
That is what salary gives you, an unlimited amount (unless you are fired) of back to back investments, you could invest this month, but can invest in October too, then on November too, then December, so if the price is low you keep buying at lower prices. I understand putting a bit aside, so if I do not want to, I put it on stable, and invest double next month.