It's me or greenhouses are a bit OP ?

Infinite wood = infinite trees = free pollution absorber ?

I think greehouses needs a little modification to be less profitable like a higher energy cost and a longer production time (trees needs to grow right ?)

I think they're fine. In a past save I made factorissimos full of greenhouses using the fertilized growth recipe to make into matter. It was not sustainable - the antimatter reactor I used to power the thing ate most of the matter it produced.

I also think that they are as balanced as they can be without reworking the entire process and complicating the recipes unnecessarily.
I tried once to increase their energy consumption while adding 2 module slots. I quickly realized why the Krastorio 2 Team has chosen not to ...

It's biofuel that's OP. My factory went from consuming the entire output of 8 fertilized greenhouses for power-station fuel, to less than 1 (plus some light oil) when I built a biolfuel refinery. Plus it has a 50% pollution modifier.

I like where biofuel is at, it's a nice intermediate between steam power and nuclear. It can also be set up remotely to power outposts too far to run poles out to. Not requiring any mined resources makes it a bit unbalanced but i'm fine with that xD