Oh yes, players in multiplayer get more of a break that you do in a multi-homeworld start. They each have their own research pools, and they each have their own reactor pools, so their energy needs don't become so much so fast. But as long as you take some more territory soon in, your energy needs start diminishing before they can become long-term problems. You just can't build to the cap in the meantime, but you don't really need to at the start in most cases, anyway.
Here's why things are unbalanced the way they are: it's actually to bring things back into balance. In multiplayer, if you had a team of players that thought as one, that acted with perfect efficiency, and who played at the top of their game, it would actually be an easier game than if you had a similar theoretical single player individual. The reason for this is that efficiency for the team at large is definitely lost in multiplayer for most mortals; while there are many advantages of having three or four brains instead of one, there's also other things that don't run as smoothly, and the game is built to compensate for that so that the apparent difficulty for most players is going to be the same in multiplayer and in solo.
Now, when you get to a single player with multiple starting homeworlds, those extra inefficiencies of trying to get two or four or whatever people working together no longer exist. It's all you, all the time. So the game doesn't go out of its way to give you extra energy and such. Multi-planet starts was actually a player-requested feature back pre-2.0, and this ultimate designed was arrived at over time with players who used it. The general consensus seems to be that the game is balanced in this mode, but that it's not at all the same game as a single player start, or even a multiplayer game. Which is sort of the goal, I guess -- it's a different game mode, and feels like it more than a little.
If you're just looking for the same game, but faster, then I suggest giving yourself and both AIs the same positive handicap, instead of having multiple starting homeworlds. Say, 200% for each of you, for instance. When all players and AIs have the same average handicap between them, it doesn't count as a cheat for achievements and what have you, and it just leads to yet another variant off the main game.