I think Riot's putting a little bit too much focus on his E, when I think the reason he's not going tank is because his other basic abilities aren't worth prioritizing. Q's slow or knockback duration/distance doesn't change, only the damage and cooldown. W only goes up by a tenth of a second per rank and he didn't even get his old W's range back. E gives more damage and makes the saplings last for a _really_ long time, which gives him unprecedented lane safety in bot lane. It's not much of a surprise that he maxes the ability which gives the biggest payoff first.
I think the rework itself wasn't terrible but he really needs some numbers tuning, and making his other 3 abilities stronger for the intended purpose of being a tank would do a good job of pushing him back in that direction.
Some quick suggestions, take with a grain of salt;
Q:~~ Maybe just a longer missile. I'd kinda like to see it made stronger overall; it's a very fleeting CC spell and it doesn't feel that good to use.~~ Raise the windup to .5 seconds from .35 and make it so that enemies in the circle are knocked in the direction of the missile.
W: Either make the cast range or the CC duration scale with level. Maybe go back to the very slow version on PBE; I thought it was kinda cool.
E: Move the AP ratio to the flat damage, say 20% AP. Make them become visible if they're in brush and you move just outside of what their trigger range is. (Wiki says they detect you if you move within 350 units of them, so say at like 400-450 units they become visible. This is mostly for counterplay to reward diligent players.)
R: Raise the total root time to 1-3 seconds. Maybe have the total number of branches go up with rank for a bigger wall, 5/6/7.