Most people will agree that it peaked some time after the EX:RS expansion and before DP. I think the most generally accepted format was DX-DP, but some say HL-HP. It started going downhill mostly with the release of DP, but LA was especially responsible. Before DP, T1KO's were virtually unheard of outside of some freak luck... but then Infernape was able to T1KO with a DRE or flipping a few heads. PlusPowers were also reintroduced, and we saw a bunch of cards doing high amounts of damage for (at the time) a pretty cheap cost. HP also went way up.
I think the most pinpointed start of the downwards spiral was around LA. Kingdra put an absurd amount of damage on the field for a single energy, and T1KO's started to become common. We also got Uxie, which introduced a new level of drawpower and the earliest form of turb-donk decks. Some would say SW created a stale format with the release of Gardy/Gallade, which is true, so that contributed to a bit of the game's current state. But basically, ever since LA's release of Kingdra we've seen cards come out to compete with it (and they've been mostly successful). SF's release of Machamp and Sableye combined with PL's release of Crobat and Poketurns created a format with decks full of donk factors. At the point, it was pretty common to donk (or be donked) at least once a tournament, whereas back when DP was first released it was unheard of.
I think the need for skill is still there, its just diluted. It doesn't seem to come to a head until T8/T4, depending on the tournament. Getting to top cut used to be a challenge, but the increase of T1 wins let more people in. Winning 2/3 games demands much more skill than a swiss match does. Also, aside from Crobat/Poketurn, I think SP decks demand a lot of technical skill. I liked the idea, but I think the way they were introduced to the format was poorly executed (especially the inclusion of Crobats).
Besides that, I think skill is being painfully reintroduced. It's nice to see, but we all know that with so many amazing sets that we gotta get some pretty bad ones. They're alright, just not as playable. When we get HG:SS-on (whenever that is), these sets will probably look much better. Even cards that seem too good right now (like LostGar) probably won't function as well in HG:SS-on, and we'll see a shift to other kinds of cards. Hearing of many of the decks that are popular in Japan right now, the format sounds really fun. Most importantly, it sounds healthy.