I'm going to have to disagree about this one: the Trainer "power crunch" is a bit messy, mostly because the-powers-that-be just didn't know how to properly balance out Trainers while they also introduced new mechanics. @_@ Yeah that is why when things get rough they have to simplify.
Nothing has approached the raw level of power of the Base Set Trainers, especially collectively; it contained not only some truly broken cards but also some that were just "kind of broken" and some that weren't broken and have basically been good cards we've seen reprinted over and over again. Here is a list of everything but in alphabetical order. Remember, if you don't know what the original version did, look it up: many received reprints that doubled as major errata!
- Bill
- Clefairy Doll
- Computer Search
- Defender
- Devolution Spray
- Energy Removal
- Energy Retrieval
- Full Heal
- Gust of Wind
- Imposter Professor Oak
- Item Finder
- Lass
- Maintenance
- PlusPower
- Pokédex
- Pokémon Breeder
- Pokémon Center
- Pokémon Flute
- Pokémon Trader
- Potion
- Professor Oak
- Revive
- Scoop Up
- Super Energy Removal
- Super Potion
- Switch
We usually only hit that level of "overpowered" when a new mechanic was put into effect later on, such as Stadiums and then Pokémon Tools. Oddly enough not Supporters; they were pretty well balanced when introduced. Note that the Neo block actually was lackluster for Trainers. The big problem was Professor Elm; as a "Shuffle and draw seven" card it was a deck staple but had the problem of being the last Trainer you could play on a turn. Your turn at least didn't end, but if you shuffle and draw seven cards and then can't use Trainers... how much else can you do? As your Bench fills, Basic Pokémon become dead draws. Whether because everything is already fully Evolved or because it hasn't been in play long enough, too often so were Evolutions. You only get a single manual Energy attachment most of the time, so Energy cards were also a high risk of being a dead draw. Plus... many of us were using a "shuffle and draw" attack for seven cards courtesy of Cleffa (Neo Genesis). I might be forgetting some really strong Trainers, but the only thing overpowered in the Neo block was probably Double Gust (as blocking the effect on your side/having a means of promoting what you wanted afterwards was common) and Focus Band (...because Focus Band).