I have two thoughts, first, if they didn't apply a penalty, nobody, including Mercedes, would have objected. But second, I feel that the penalty wasn't for the initial re-entry back on track, but the final squeeze towards the wall. It does happen in a split second but it's that style of driving that Vettel has, that small extra unnecessary move as a reaction being in a disadvantage position. Bit like Schumacher and Rosberg had as well. Bit nasty.... and for that, I do feel that at least a reprimande was in order. If you look at the Ricciardo/Hamilton moment at Monaco in 2016, he left him precisely 1 car plus 2 inches space.
Anyway, I don't feel Vettel was robbed of a win, Hamilton forced him into a mistake and he was lucky that he didn't put in the wall. We were robbed of a potential epic battle for the last ten laps.
anyway, another missed opportunity from Vettel.