Tolerances of caps, resistors, pots.. Different power tubes, different preamp tubes.. Old/bad caps vs new caps.. And they aren't dialed in at the exact settings. I've had Rev G's that sounded better than Rev F's. I had modern Multiwatt's that sounded better than Rev F/G. I've had Triples that sounded great. I've had a Roadking that sounded better than all of them. They were all great for rock and heavy metal straight up. They all needed a boost for death metal or modern tones. They all sounded better than the Shitlander. Mesa amps are all over the place with consistency that it's fitting Gibson bought them. Just like you have to try out 10 Les Pauls to find a good one, you have to try out 10 Rectos to find a good one.