Here's how I feel about plants.
Here's my feedback:
The healing plant allows laners to take bad trades and not have to back.
The blast cone allows players to overextend and not lose anything.
The vision cone allows teams to have bad vision and not be punished by having to facecheck.
Let me give you an idea of what type of player I am. I'm a diamond support who has bad mechanics and has climbed through map knowledge, good warding, knowing my enemies cooldowns, and not making stupid plays. I roam a lot. I ward aggressively. I track the enemy jungler. I track the enemy support. I'm the one pinging the top laner's flash and reminding everyone that it'll be back up in 30 seconds.
Despite this, I do not know nor do I care what the little partially grown plants mean, or about how they're not RNG, or whatever. It's simply not anything worth tracking, because there's no benefit.
The thing about plants is that they lower the skill ceiling of tons of stuff. Invaded the enemy red buff but Warwick is stronger than you? blast cone out, nothing lost. Enemy been meticulously warding Baron for the past two minutes, and now you're forced to facecheck the potential bait? Never mind, just hit the vision cone. Failed to track Syndra's XP and she suddenly chunked the hell out of you at level 6? Go collect some honeyfruit.
In these three scenarios you've saved your flash, your support, and your teleport. In all three of these scenarios you deserved to lose those things. And don't tell me you made that play knowing the plant was gonna be there-- you just got lucky. You weren't watching the half-grown ones either.
Again-- these things aren't the worst part of League. I wouldn't even mind that much if they stayed. I just think that they lower your ability to show your skill by a little bit, and they're simply another get-out-of-jail-free card that most people don't bother to track, they just use them as they show up.
If you asked me how to fix plants, I would make it so you had to deliberately plant them. Once planted, they would grow over a set amount of time, after which either team could use them. At any point during the growth cycle someone could come along and stomp it out, preventing its growth. This could function in a similar way to capturing a point on Dominion for planting, and capturing Skarner's Crystal Spires for destroying. After the plants were fully grown, if they were unused after another set amount of time, they would die. This, in my opinion, would allow them to have some kind of prediction involved, instead of basically being RNG.