Probably, but the last time I really cared about load times enough that interlacing or progressive downloading was an issue would have been back in the early 90

Probably, but the last time I really cared about load times enough that interlacing or progressive downloading was an issue would have been back in the early 90s on dialup and well before progressive JPEG was even a thing. IIRC, watching a JPEG paint on a 386/25 or maybe an early 486 was something that could likely be measured in full seconds or tens of seconds, not tenths of seconds.