It sounds like waiting until you have Medieval Infantry would be a good idea. Hoplites are the equal to Swordsmen without any bonuses. If they're on a hill, they get a 50% bonus, if the city has walls, another 50%, and since they'll be fortified, that's 25% more... so you are looking at a 75% to 125% bonus - a strength of 5.25 to 6.75 versus your 3. That's a big difference. Generally, if I'm warmongering in the ancient age and can fight someone other than Greece, I prefer to.
The difficulty levels between Civ versions are not necessarily comparable to each other. In my opinion, Civ5 is definitely the easiest Civ for the difficulty levels. I found it pretty easy to run over the AI in my first game at level 5 (can't remember if that's King or Emperor), whereas in Civ3 I mostly win on Monarch, and in Civ4 I usually win on Noble. So, going down a few levels and still struggling isn't too surprising.
Against a couple regular Spearmen on flat land, without walls, 5 Swordsmen should be enough to guarantee victory, and 3 would have fairly good odds. But you're facing a tougher opponent.