The last time, when we had red herrings and suspense for the sake of suspense, Chromia ended as a braindead terrorist. I'll take logical plot unfolding than a suspense out of the left field when other options are more sensible. Though with Chromia some readers anticipated it, still it was a very artificial plot and character motivation. Likewise, if during the Enigma and Blackrock arcs Barber solved it in any other way than Onyx Prime being responsible for the facsimile, I'd call ****shit. As soon as the suspense is gone it would simply feel very phoned. It wouldn't be any different with Roller not being Tarn. What's the point of even showing Tarn's chin under his mask when it looks like Roller's, but he's not the Roller? Or him being given a copy of Megatron's writing? Not to mention Roller's jealousy towards outliers and Tarn's phrase about "uncovering his potential"? You don't gradually introduce hints in such quantity to bail out of it and say "surprise, it was someone else all this time". Especially if you realise that Ambus wasn't even shown in the book in any retrospection save for his arternative version from the Functionists universe... Mentioned as often as he may be, he's a non-entity in terms of his actual presence.