Longsword + siege can work against Aztecs defensively in early castle age but that has a bunch of its own problems. Poor scouting, enemy boom, set up for jaguar counter, eagles sniping siege, etc.
As of right now longswords cost to much to tech into given their ability to effect positive trades is very limited. E.g. it costs 150 for supplies, 215 for LS unlock, and 175 for a second barracks. If you’re going to spend that kind of villager time you might as well just make a castle for samurai to avoid the jaguar face rolling you later on. 1 castle samurai produces as much as 3 barracks making longswords in terms of army value so you don’t need a second castle anytime soon. Granted samurai are a bit overpriced (40% more than LS is a bit ridiculous, only made reasonable here because Jaguars are also overpriced) but the point is production isn’t the problem.