Here's some actual measurements. Sitting at my table the other day transmitted to the local DMR repeater. I watched the results using the "Last Heard" window on the Brandmeister website. The Brandmeister window displays a bunch of useful things, including the signal strength of each transmission heard on a repeater on the network. It's a great tool for diagnosing issues with DMR.
Without moving from my chair, I swapped antennas back and forth. The long one was a 17 inch TIDRadio 771 (not sure if it's a knock off or privately branded by Nagoya) on a 70 cm DMR HT and the short one was the 6 inch rubber ducky that came with my HT. Using the longer antenna, when I transmit to the local repeater, which is 16 miles away with lots of buildings and trees in-between, I get an S8 reported by the repeater. Using the standard rubber ducky I get an S6, which is 12 dBm lower. In my opinion that's not insignificant.
During our weekly network check-in, using a Baofeng and a 24 inch antenna, a guy 45 miles away hit a 2 meter repeater at the same site.
I am impressed by the difference the longer antennas make. I'm sure there's something much better, but for the price, It may be good enough.