Old Jeeps were notorious for poor heaters. The heaters in my 2014 Rubicon and 2018 Cherokee are capable of smelting iron ore. Five minutes of warm up with the defrosters on high will pretty much clear any snow and ice on the windows (and on the ragtop Rubicon, will usually melt any snow on the roof).
No Kidding on the heaters in the new jeeps. you can burn your hand touching the vent.