Okay, here is where your mistake lies. Every new playable aggro card replaces another aggro card. Forbidden Ritual replaces Implosion. Possessed Villager replaced Argent Squire. But board clears and removals DON'T necessarily do this. If you gave mages another full board freeze of some kind, you wouldn't necessarily see Frost Nova and Blizzard getting cut. Freeze Mage would just get crazy af because now it can freeze your whole board 6 times. Every major board clear, heavy healing, or efficient and powerful taunt has a huge effect on the pace of the game for any associated classes. Aggro cards don't necessarily do the same, because they just incrementally improve an aggro deck by swapping one minion for a slightly more efficient one.
So you're saying because new aggro cards replace old aggro cards, it's okay? I'm really confused. Because you seem to be saying freeze mage sacrifices nothing to get another board freeze (they already often don't run cone of cold so not sure why you think they'd run another anyway). Whatever freeze mage would cut to run another board freeze acts like aggro replacing one of their old cards, for whatever that is worth.
You're just spelling out a huge problem for the game and acting like it isn't one. Because aggro cards getting more efficient versions of old ones is a huge problem, one that pro players like reynad identified as an issue back in classic. And a problem that showed itself being an issue for many people when secret paladin came into play. And one that shifting from wild to standard is supposed to address at least in part. "Just" replacing an old card for a more efficient one is essentially power creep.
I understand and agree now why people hoped for more nerfs. Because decks like zoolock and freeze mage just plug in their new "slightly" more efficient cards and kept on trucking as if nothing really changed.
I am surprised to find myself agreeing with kripp regarding aggro decks. These super efficient 1 and 2 drops, mainly the 1 drops to be honest, are problematic, but not because they exist, but because there are too many of them. Imagine if leper gnome wasn't nerfed, what shit state the game would be in.