One of the issues as Frost pointed out, is how many types are represented by each energy.I dont understand the love they have for Lanturn, 7 cards since Sun and Moon, Reuniclus havent appearead at all since Fates Collides (XY) and dindt the spoon bending guy retired his sue agaisnt Kadabra? When Kadabra will return? GO Set sound like was the perfect opportuniny to bringing back being a Kanto related set pretty much
Fire, Lightning, Steel and Dragon only represent themselves - and Dragon isn't really a fully fledged one either.
The others are 2 or more:
Grass - also Bug
Water - also Ice
Fighting - also Rock and Ground
Psychic - also Ghost and Fairy
Colorless (Normal) - also Flying and Dragon
Dark - also Poison
I'm not sure there is a sheet anywhere that breaks all the 900 Pokemon into what energies can represent them.
But, Lightning and Fire normally have fewer new Pokemon each generation whereas something like Grass and Bug are big groups on their own and are combined. That's why Lightning Pokemon get loads of cards and one of the reasons why early Dark/Steel Pokemon like Magnemite got so many cards.