Not only will a propane torch get vastly hotter, but it also has orders of magnitude more energy.
This torch is 50,000 BTU (presumably per hour). It’s probably much bigger than your average propane torch, so let’s say the average torch is 10,000 BTU/hr.
10,000 BTU/hr is approximately 2.9KW
The battery pack for that tool doesn’t have a watt-hour rating, but I found a link on the web that said that their standard pack was 54WH. Let’s be generous and say this pack is 100WH.
So, the the torch will put out more heat in 2 minutes than the heat gun will in an hour, and in an hour, the heat gun battery will be dead.