I, personally like to use my team. But if I tried, I'm sure I can beat the Elite Four single-handedly.
In Crystal I once used a LV100 Blissey against the Elite Four, which didn't work, as it was terribly weak then.
I haven't tried yet, since I never have had a Starter to reach even Level 70. I'll try to use my Sceptile with Miracle Seed, the Modest Nature, the attacks Attract, Double Team, Dragon Claw, and Giga Drain/Leaf Blade, and 252 Sp. Atk. EVs, 6 Sp. Def. EVs, and 252 Speed EVs. That's for Emerald.
For FireRed, I will try to use my Charizard. It doesn't have specified EVs, but it does have Fly (forgive me, I like to use it), Dragon Claw, Flamethrower, and Earthquake. Currently it's in its 60's. XD