Vinyl - Warm without underfloor heating - Warm with underfloor heating?

This statement is unfortunately not correct. "higher thermal resistance" requires higher flow temperature and thus higher consumption.

maybe technically not entirely correct to equate these. Practically in its effects regarding efficiency and thus costs probably below the threshold of perception. Or am I mistaken here?

maybe not entirely correct technically to equate these. Practically, in terms of impact on efficiency and thus costs, probably below the threshold of perception. Or am I mistaken here?

So the correlation, lower flow coefficient -> higher supply temperature at the same room temperature is quite clear.
And the statement that it just takes a little longer is wrong.

Whether it strongly affects consumption then naturally depends on the heating system.
With a heat pump, it will indeed make a difference.