I clicked on this thread thinking that it was about the general state of the meta, and definitely agreed with the title. I really didnt agree with the contents, which seemed more like complaining about assassins than anything else. Personally, I think Riot has been doing the opposite of "buffing things to match it's power", and has instead been nerfing things in a very unintuitive way, particularly when it comes to major changes.
Crit ADCs too powerful? Nerfs and item changes.
Gold funneling too much? Direct nerf to gold generation when farming lanes.
Jungle paths too regular and too fast? Rework the jungle, and make it more difficult.
I don't even think your example is even that good. Zed did 500 damage by hitting TWO shurikens using his shadow, plus the rest of his combo to finish you off. Is he strong? Sure, when he's able to do what he wants. Zed's currently sitting on a sub 50% winrate in pretty much all divisions, and remains a fairly popular champion. Pretty balanced. Zed's counterplay comes from zoning early, playing cautious later, itemization, and support from your team. He's not some insane, counterless champion, and while yes, one of his hardest counters is fairly uninteractive, he's not some completely balanceless, uninteractive champion.
Ignite was buffed in 8.6 as a response to the prevalence of mages in midlane who would farm for ages, were unresponsive to poke, and difficult to touch by assassins. Teleport, ghost, and heal were used more over ignite. In response, ignite was buffed, heal was nerfed, and several assassin items were buffed, and mage items took a MASSIVE hit. Now ignite is more prevalent, taken more often in botlane, with reasonable frequency in top, and often in mid. But teleport is being seen used in more places, barrier is cropping back up, and responses are developing naturally.
You will always have a meta of things that are powerful, a meta of things that need to be nerfed, and a collection of things that will need to be buffed. It's inherent in playing a competitive, asymmetrical game like league.
...That being said, I agree with the title of your post.
I think league is really lacking in counterplay due to the direction things are currently moving, how Time-To-Kill is growing shorter and shorter with each season, it seems. Every champion that is released or reworked seems to become faster moving and harder hitting, most of them becoming absolute monsters within a few patches of release once people figure out how to play it.
Irelia rework, Aatrox rework, Swain rework. All got buffs, extra CC, became more mobile, and were prevalent in the meta, at least for a few patches.
Look at the champions released. Kled, Pyke, Camille, Kayn, Zoe, Taliyah. The last "True Tank" they really released was Ornn. Before that? Tahm Kench
Riot has been releasing more crazy champions, with more "riven-like" kits with each release and each rework. Kits that are hard diving, fast moving, high damage. They're fun to play, and fun to watch, but not really fun to play against.
That type of kit, the 'overwhelming offense' is what I think is killing counterplay. Most of these champions jump on top of you and kill you in one rotation, and they're everywhere in the meta right now. They're hard to peel, hard to shoot at, and hard to survive. Riot has begun to bring them into line and tone them down, but this overall trend towards high TTK combined with CC and mobility is unsettling, and hard to play against. I can deal with a Zed. CC him in a teamfight, and he dies instantly. I have problems with things like Irelia (at least, when she was strong.) Stuns your entire team, kills two, gets CC'd, loses only half her health, and kills one more before finally dying. Or when Zoe would sleep a champion, only to seconds later to nearly one shot the tank who was bodyblocking.
To me, the concept of no counterplay really emerges when I simply don't have options. There are simply things in the game that you can't fight, can't run from, can't itemize against, can't play around, and those to me are the uninteractive, broken champs. A mage and a CC support could take on a Zed. A mage and a CC support will lose hard to your Camilles, your Kleds, your Udyrs, and champion of the same vein. They tank the burst and CC, then charge through and beat down both the mage and support. Itemization doesn't help, they have few hard counters, and can both lock you down and one shot you. This combo of good CC, good damage, good mobility, and good durability is really hard to counter and hard to play against. But, again, I think Riot's starting to bring it inline.
I really think we just need more options. Several new tank items, a mage item or two to help things along, and maybe some buffs to ADCs too. A new shutdown, lockdown oriented champion or two with good CC would be nice also.
In the end though, I still agree with what you have to say. There's too much damage. Too much offense. Not enough counterplay.