The pain in Humira comes from the citric acid I think, which lowers the pH of the shot. But if the biosimilar does not use citric acid then I would assume the shot would hurt a lot less.
There are other anti-TNFs on the market, many of which you all have heard about - Cimzia, Simponi, which hurt a LOT less. Simponi is basically painless according to both my girls. Cimzia hurts, but much less that Humira. My daughter said it stings and it's very thick and the injection (only a syringe, no pen) takes a long time. But it still hurts a lot less than Humira.
But anyway, the point is that clearly they can be formulated without citric acid or whatever it is that lowers the pH and makes the shot really burn.
My daughter is now on daily shots of a different medication but they are basically painless and she does not mind them at all. So it really depends on the medication - the poke is easy to deal with, even when it's every day.