Firstly, to answer your questions regarding those EXes - correct about no weakness/resistance being applied to the bench. And I'm not sure why, but some people actually use Florges as a main attacker, even though it can't really OHKO any other EXes - although this will change when the next set comes out, as there is going to be a Stadium which expands both players' maximum bench sizes to 8.
The examples I gave aren't even some of the strongest Pokemon EX these days - I gave the examples I did because they don't Mega Evolve, and I wanted to introduce you to the power creep one step at a time. Nowadays, many of the most popular decks involve Mega Pokemon, such as Mega Manectric, Mega Gardevoir, and Primal Groudon, for example. Mega Pokemon evolve from the corresponding Pokemon EX, and normally Mega Evolving ends your turn (so you don't get to attack with them right away), but if they have a special Pokemon Tool card called a Spirit Link attached to them, your turn does not end.
Regarding the evolution of the game's meta and structure, as well as the power of evolved Pokemon: Rare Candy was first introduced in the Sandstorm expansion in 2003. Up until about 2 years ago, that restriction you see on the most recent print - the fact that it can't be used on a Pokemon that was just played or on your first turn - did not exist. So, you could play a Squirtle down and immediately evolve it into a Blastoise, potentially even on the first turn of the game. For this reason, combined with the fact that the current incarnation of Pokemon EX did not exist, Stage 2 decks have been quite powerful for most of the game's history.
Pokemon EX were also first introduced in the Ruby/Sapphire generation, but at that time, they were the correct stage - for example, Blaziken ex, one of the most powerful cards in the game at the time, was a Stage 2; nowadays it would be a Basic like all other EXes. And EXes were certainly more powerful than non-EXes then, but not to the degree that they are today - for example, here's a Rayquaza EX from back in the day compared to the current one. When the Diamond/Pearl generation came around, Pokemon ex were replaced by Pokemon Lv.X - these were sort of like Mega Evolutions, but your turn did not end when you played them, you could only Level Up a Pokemon if it was your Active Pokemon, and a Leveled Up Pokemon could still use the attacks of its previous form, unlike Mega Pokemon. One example of a popular Pokemon Lv. X was Flygon Lv.X, using its Poke-Body along with the attack from this Flygon.
The Black/White generation replaced Pokemon Lv.X with Pokemon EX again, except this time, Pokemon EX were all Basics, and were way more powerful. These new superpowered Basics, combined with the nerfing of Rare Candy, shifted the metagame from primarily Stage 1 and Stage 2 decks (though some popular Basic decks existed too, from time to time) to a state where gigantic basics were pretty much the only viable option. For a couple of years the game was incredibly stale. Now, however, it is finally starting to get healthier again, and we are seeing a wider variety of successful decks, thanks to a slew of incredibly inventive card effects introduced in the past 2-3 sets.
