Maokai's slower W was actually a huge buff...
Against any champion with a blink, dash, or flash...
Now you have to WAIT for it to land before you can blink/dash/flash away, otherwise it's extremely slow speed follows you and roots you, giving him a much better engage and lockdown.
Obviously this was something old maokai could do, but the thing was, it was something he WANTED to happen, as the team's engager/stick champ. But it was much more difficult.
And it is now much easier to do because...
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most people react instantly, and thus try to dodge an immediate engage, and now that it's slower the fast reaction actually works against them... taking a longer time to get to the champ than before.
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if you wait for it to land first, which was (in most cases) the correct response to old Maokai, you're now more vulnerable to enemy damage/cc in the meantime, which means a much easier death at their hands.