I mean, that is what a “real” lightsaber is too. Contained plasma. So a butan flame is not “that” far off. Now to find a way to shape the flame with magnets instead of relying on laminar flow and you have as close to real lightsaber as you could get.
While the hacksmith sabre is as close to the movie ones it is not a light sabre. Because you would need a device capable to generate a laser strong enough to cut through steel and a gravitational pull that pulla back the light so you don't shoot through the whole galaxy.
And if you have the technology to build sth like this a light sabre would be the stupidest thing to build.
Pretty sure that lightsabers are described as being plasma-based even in-universe, rather than lasers. I get that the name can be misleading in that sense.