"Ever one of them came out as if they had already been broken loose."
Jaxs, there is probably a good reason for that; I've used the trick a few times, pretty much ALWAYS works. The reason was explained to me decades ago, by a guy that was at least as old as I am NOW...
When you heat a stuck fastener, the better you can localize heat to ONLY the fastener (NOT the threaded hole it's in) the heat tries to expand the fastener - but the larger (usually) mass of the threaded hole doesn't allow the bolt to expand in DIAMETER, so it mostly expands lengthwise.
Cooling is a different matter - when the heated bolt cools, it shrinks in BOTH directions - making it SLIGHTLY smaller diameter - this tends to break loose any rust bond, and it also allows any penetrant easier access to get between male and female threads. (If it's even necessary, usually not)
Doing this can get tricky for smaller fasteners, unless you have something like a jeweler's torch - the welding a nut method (especially with MIG) becomes the easier way, but the end result is the same.
The guy who taught me about this was a gunsmith; same problem, but a smaller scale - in order to get the heat local enough WITHOUT ruining the gun, he'd modified a small spot welder so that one electrode had a very LARGE surface, and the electrode that touched the actual stuck screw was a pencil point.
NONE of which helps if somebody has left hand threads and doesn't know it tho
... Steve