I've gotten barrel nuts off of numerous PSA uppers without issue. Sure, some take a little extra umph, but that's not been limited to some PSA. Worst I've seen are RRA.
If you're working with metals and you don't know the value of heat, you should rethink working with metals.I used this and a ton of force (not heat IIRC)
Nah. I’ve use heat with other applications, auto, plumbing etc., I don’t see why to add it ‘by default’ when other tools can get it done quickly. Getting truly stuck or knowing the battle ahead is a whole different matter. As someone who used to over torque things I’ve slowed down enough to not go “all in” by default.