True, that. Though I believe there are rebates now thanks to recent fed'l legislation. PLUS the heat pumps offer A/C in summer. That was the kicker for me. I put a mini-split in my upstairs ADU after the tenant mildly complained about the August heat two years ago. Works great, tenant loves it and saves me about $300/year. Cost was $2500 (after rebate), so payback just over 8 years. Not too bad. I was so impressed I installed them in my duplex rental units. Payback harder to calculate there, as I don't pay the electric myself. But it makes the units more desirable (especially the A/C, now that Portland summers are getting hotter) so if the heat pumps reduce turnover it'll be well worth it. FWIW my units are in the 550-700 sq ft range. The costs for a house would of course be higher (my sister had two installed, one for each floor, for $9k last year).
If you WERE looking to BTD, a heat pump would be a nice option. Totally understand that the payback probably isn't there (though supposedly they're better for the planet since they use less energy).