I already know that the answer is "depends". Depend if the hardware is low-mid or high hend. So, I try to re-formulate: is 100K concurrent polycount in a 3d game for smartphone too much ? How many is it a good compromise ?
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CPU, GPU capabilities, and screen resolution varies too much, even 2015 onward.
And then it still depends on triangle shape, occlusion, OS version, texture types, size, quantities, vertex and fragment shaders and so on...
You need to buy (or borrow) phones and test your game on specific models and then hope for the best.