This weakens Riven's early game, but allows new Riven players to prosper without doing the weird animation-cancelling technique, which is more of a bug than an actual feature. Simply by building attack speed, you can easily perform the three Qs faster than before.
Animation canceling was actually an intended feature Riot specifically added and mentioned in the patch notes.
Also - why should Riven have a weak early game?
One thing I really like about her ATM is that, as the lone-wolf top-lane 1v1 duelist class (Fighter), she's actually really solid when you're a lone-wolf/top-lane/trying to 1v1 when everyone's split up and you can 1v1.
It's kind of annoying playing a fighter like Aatrox that's not super great early-game and easily bullied by ranged champions like Ryze or Vlad just because range offers a huge advantage when dealing with tower aggro and minions.
Then you build items and become useful in 1v1 situations when everyone wants to team-fight, which really raises questions as to why you'd even bother when someone like Vlad or Ryze can AoE ~50% of an enemy team's collective health with the same items.
I'd much rather see other fighters get put on Riven's level where it's more a strong early and if you do well you can be solid in team-fights, rather than having useless useful qualities due to conflicting with the game's progression.