If you have been participating in the Regular events, you’ll find that you have at least 3 fairly solid teams and partial teams in addition. Getting up to 5 teams should not be much of a stretch. Sure, they may not be the strongest teams on the planet, but remember that everyone is in the same boat on this or nearly everyone.
When I started playing the game, I started out by saving one of every hero 3 star and up. As time progressed and I did some 10 x summons for events etc, I I would save up copies of the heroes when they came up and then use them to raise the power of the originals. yes, this took forever, but I wasn’t really using the heroes and had my main group. Over time, I ended up developing a broad number of heroes. Now as Alliance wars approaches, I find myself with enough heroes to make at least 5 solid teams of Heroes.
For those who go the cashless or nearly cashless route, you can do nearly the same thing with your Training grounds. As you summon a copy of a hero you have, mark it as a favorite and when you get enough copies, use them to raise the power of the original you had saved. Yes, this takes time, but it is the smart way to go.
I hope this helps.