I don't think it's a secret that there is way more damage in the game than their used to be. Between keystones, items like Stormrazor and Duskblade, and just champion kits in general, damage is frankly insane. One of, if not the biggest contributor to this, is the way abilities have been managed over the last several years.
Oh so long ago, abilities used to have mana costs. A lot of the time, those costs were not trivial, and on the champions who had very low or no mana costs there was **supposed ** to be a tradeoff. For Kat and Garen, that tradeoff was long cooldowns, for spammy abilities the cost was usually lower damage or no other effects. Utility was not attached to every spell, and most kits did not have 4-5 or even 6 ways to deal damage to an opponent. I remember Brand coming out and thinking how insane it was that all 4 of his abilities dealt damage, and he had a passive that dealt damage. Now guess what, all of those things not only deal more damage, but he can use them more often because CDR is so easy to get, and they cost him less to use. This is huge, because I really wouldn't have a problem with pillar of flame dealing 150 damage to me at level one if he couldn't do it over, and over, and over, and over. Now, not to single out Brand, but there are TONS of champions that this has happened to, and I personally think it's time to address it.
CDR needs to be looked at as a stat, and abilities need less damage, higher costs, and/or longer CDs, or the insane damage meta will never end. By increasing CD's, you increase time to kill in most situations. Increasing time to kill make playing a sustained damage champ possible (ADC buff in disguise). It also makes tanks feel good to play, and they no longer have to be CC burst bots who also explode the second they get touched. Everything about the game would be better if abilities had real costs to using them.
When did this start happening? As much as I hate to say it, I remember when Darius came out and his mana costs seemed to be nonexistant. He could spam Q, always use his W, and grab you whenever he needed to. It was a problem for top lane, so they started buffing other top laners, and the snowball rolled. I honestly think this would be extremely easy to fix, and make the game FEEL so much better. But I don't think it will happen, because Riot seems to think no one wants to play a game where 360 no scope oneshots aren't meta.