Not just the RF stage, but having only two IF stages made the Muntz sets unsuitable for fringe areas.
Regarding digital converter boxes, their analog RF output level is completely independent of input level. All set top boxes: cable, satellite, VCRs, D/A converters, game consoles, media players, have RF output levels within a range established by the FCC in the early 1970s, chosen to provide a noise-free picture without excessive interference to other equipment.
Per FCC part 15.115, with 75 ohm interface, this is 6 mV at peak sync for a master antenna system or cable system terminal device, and 3 mV for set top boxes. The audio carrier is limited to 1.34 mV or 0.67 mV, respectively.
https://www.govinfo.gov/content/pkg/...-sec15-115.pdf