they do usually take longer in soil the heat mats help. The best soil starters are the ones you find in your soil bin you have forgotten about those are strong starters lol I agree If I buy them its towel for sure.
Never again will I dig for a bought seed with a chopstick to see what happened to it.
paper towel..'
If its good it'll go. If its bad it'll stop. If its tired it'll stall. Flip the towel to check...or...play mini excavator
Tried the worm bin vs paper towel recently. Towel won. YMMV