Each plant is an entity, it’s not actually concerned with the mesh limit or the plants around it.
The mesh limit ensures that the number of meshes doesn’t crash the client, or the server processing them. It’s in place to ensure that each mesh can perform it’s duty well.
Each tick of each plant (organic or inorganic) contains an RNG component, so if one plant consistently makes bad “rolls” it can look like it has been singled out in some way, but it’s not.
The (Stated) reason for this is that it would have taken considerably more stored data per-plant to track it’s history of growth or aging, and the devs were unable to allot this amount of storage, when players can plant so many plants on a world. It’s less expensive to simply look at the plant’s current state and roll for advancement.
Ironically then your plant that withered so much faster than the others is simply having more “success” at aging 
You could consider each attempt at growth similar to an attempt at getting a forge boon, then. I think it was luca that explained this very technically I’ll see if I can find it.
I Can’t quickly find the particular post I remember however in this thread there’s some good discussion of the math and the reasons:
Basically though, the only thing stored about any single plant is it’s current condition. This includes the current stage of growth and fertilization.
At each “tick” the environment is evaluated, and the appropriate rolls are applied to the plant. The new state is stored, and everything goes idle until the next “tick” is calculated.