I disagree with weakening attacks when used with low energy, as to be honest, some of the best turns are those where you're living on the edge with 1 chill and 2 attacks per round. Furthermore, it removes the ability to do super cool last-ditch-attack combos, which is the primary motivation for combos to exist at all (awesome last-ditch shit). Also, you need to realize that energy is a logical anime interpretation of in-game PP. In-game, your attacks don't get weaker when you have only 1 PP left in them, they are the same strength as they always are. To me, intentionally weakening Pokemon at the end of their game takes all of the fun out of those last rounds, and ultimately detracts from a fairly important part of battling—pinch battling.
Well, first of all, I found a reason to use a combo outside of last-ditch attack: Fly (and, by extension, Dig, Dive and Bounce). Had I used an ordinary attack that turn, my move would have missed. Because I used a combo that hits at the same priority as Fly's attack and am slower, my combo hits.
Furthermore, you're right that EN is equivalent to PP and that having 1 PP doesn't make your attacks weaker. However, 1 PP is sufficient cost for the attack, whereas 3 EN for an attack that costs 10 EN is not.
And pinch battling? That's for when you're down on HP and your opponent is going to KO you with his next move. If you're on a decent amount of HP and hardly any energy, then you played inefficiently and should be penalised for that.
I prefer to think about those last ditch efforts in terms of adrenaline. When you are about to faint from exhaustion in real life, you get a burst of energy—called your second wind—before collapsing. This is a
real phenomenon. Any attempt to claim that "using your last-ditch move combo is unrealistic" is, amusingly, unrealistic. Heck, this even happens frequently in the anime.
So, how come the second wind doesn't last long enough for the pokemon to continue attacking after it has actually run out of energy? That wiki article makes it sound like the second wind phenomenon lasts for more than a minute (which is the longest an attack or combo could possibly take).
And again, just because it happens in the anime doesn't mean we should make it happen like that in ASB.
3 energy is 3 energy, not 23 energy. If it were 23 energy, then it would be written as 23 energy. If you want more energy, use a chill. If you're taunted (and so can't use chill) and somewhat low on energy, then use weak attacks that only cost 2 or 3 energy until you can chill again. And if you run out of chills, then ... well, sucks to be you.
However, there is another way we could handle using attacks when you don't have enough energy to do so: simply make the attack fail altogether (regardless of what kind of attack it is) and make the mon faint. I don't expect this to be as popular as the other suggestion I posted but it's a possibility. Or we could simply have the total fail apply to non-attacking moves and the attacking ones could use the BP*(current EN/required EN) formula.