Suggestion for Plant Levelling.

I believe that the biggest issue truly with levelling as of right now, Is that it is spread across tier 1-3 separately.

If you level up a peashooter, it won't then also upgrade Repeaters and Gatlings.

I think personally, levelling should be for base plants, and the way I see it being done is:
- Level up a peashooter, the effects on it will be low HOWEVER
- All peashooter merges will then be affected as well with a % increase depending on what tier it is.

If for example again, you level up a peashooter... firstly the peashooter itself would get a small buff in the form of maybe, 5% more damage. The thing is now every merge that includes peashooter, would ALSO get that same damage buff with a multiplier depending on the tier of the merge, so tier 2 would get 7% and tier 3 would get 10% or whatever works best for balancing.

The interesting part would be that, take peanut for example, only the peashooter aspect would level up (its damage), so if you were to want to upgrade its health, you would then need to go and level up your wallnut.

Personally this just seems like a more interesting system, as you would be able to choose exactly what playstyle you want to go for, there's less overall plants you would need to level up and tier 2 and 3 would feel appropriately scaled in comparison to base plants.