For those who have been around for quiet a while, I'm talking beginning of R/S or earlier (at least Neo era for me), the fact is that the amount of energy in theme decks (if not the type) was typical of decks at that time, anywhere between 20-24. My old Rain Dance deck ran about that much for all of the Pokemon.
To be fair though this was long before the game had so many trainers, like it does now. In those days trainers were pretty basic with card draws, healing, energy removal/denial, some Pokemon search stuff and the occasional fossil thing, along with later on some stadiums. But they didn't have several cards to the same thing, like they have with Juniper and Sycamore, or having as many variances in pokeball cards like now, nor at that point had they seperated trainers out like they do now (basic, supporter, items), At that point Mysterious Fossil was for all fossil Pokemon and not given individual fossils. In short trainers were a lot less 'complicated' in those days and so having that kind of energy wasn't as hard to see.
That being said, it's true that with the possible exception of fairy energy, players who have been in it for a while should have all the energy they will ever need with no way to get rid of them short of out right throwing them out, making it kind of annoying. In another set or two we might have all the fairy energy we need too.