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Devkure It may not be polycount per se but in fact the amount of details in general (i.e. the transparency texture). Hard to tell from your screenshots. It's not really clear what that bush is made of.
In general, you have two options. Either adjust the design/geometry of your meshes so they lend themselves to visually pleasing outline rendering, or render outlined and non-outlined things into separate viewports and do a depth-composite. The former is technically much less troublesome with potentially much better looking end result.