Given the length and often meandering nature of this thread, I really shouldn't have brought the subject up here.
I did though, and my common sense didn't kick in until it had already been up for well over 12 hours, as well as having had a response. So I will comment, hopefully just a little more.
At a glance, the easiest solution seems to be direct adaptation of the video game Types to the TCG. Unfortunately, this is easier said than done, since so many other mechanics are lacking.
1a) In the video games, attacks have their own "Type", and matching it to the Pokémon gives a bonus to the attack.
1b) In the TCG, attack Type corresponds directly to Pokémon Type... so a Pokémon with an off-Type attack faces the same Type-Matching situations as one with an on-Type attack.
2a) In the video games, Weakness and Resistance are more varied in execution; Pokémon can take quadruple damage, double damage, unmodified damage, half damage, or be immune to damage from another Type... and can have such relationships to as many Types as the Pokémon's own Type (or Type combination) would require.
2b) In the TCG, Weakness is currently x2 or non-existent (barring certain card effects), and Resistance is -20 or non-existent; barring a few older mechanics, a Pokémon can have at most one Weakness and one Resistance (and never has hard more than two of each). All of these are simplified and fundamentally different relationships.
3a) In the video games, each can react to each other Type differently, usually possessing multiple forms of Weakness and Resistance.
3b) With some Types being merged in the TCG, sometimes a Pokémon finds itself in a situation where it should be Weak to some members of a TCG Type, but neutral or Resistant to others.
4a) In the video games, attacks have a limited amount of times they can be used based on each attack's "PP" score. That is to say, starting with "fresh" Pokémon you can use the attack(s) of your choice until they run out of juice.
4b) In the TCG, there is no limit to the number of times a Pokémon can use an attack... provided the Energy requirements are meant and the attacking Pokémon hasn't been KOed.
5a) The video games not only typically have higher HP scores (when Pokémon are fully realized), but also have the interaction with the Defense and Special Defense scores in damage calculation.
5b) The TCG HP in the current wave of cards are such that most Pokémon, regardless of Type, can at worst 3HKO each other, and usually 2HKO each other (with OHKOs common when Type-Matching is favorable). Big hits are no stranger to the video games, but see earlier comments about how attack and defense mechanics differ.
6) You need distinct colors for Types given how the TCG functions.
7) You may need distinct Energy Types given how the TCG functions.
8) Frankly I am of the opinion the video game system is pretty bad for Type taxonomy. A lot of the smaller groups sort of make sense; but the problem is when they are all combined you have very dissimilar aspects being held up as 'Type': channeling an element is treated the same as being composed of an element, chi manipulation is on par with those, psychic abilities are on par with those, using poison is on par with those, method of movement (flying, swimming, etc.) seems to be on par with those, and that is before we get to odd things like having both "Ground" and "Rock" Types, or how Ice-Types seem to be one part attacking with solid state water and another part dealing with lowering the subjects temperature/attacking with "cold".
tl;dr: The overarching issue is the video games and TCGs being games with very dissimilar core mechanics but a "skin" of Pokémon applied to each causes numerous problems, but a big one here is how differently damage is calculated between the two.
