I don't think Gomes or Vlasic have the defensive acumen in any position.
However, in Silva's ideal 4-3-3, he's either got a true 6 with a box to box type, or twin CM/DMs.  The third mid isn't really a 10, they aren't quite that high - Siggy has looked good in the role with Morgan sitting & Gana flying around winning balls, pushing it forward.  Gomes would be with Gana as part of the first 4-3-3, but I personally HATE him in that role as he's terrible defensively both sitting or winning balls.  So acquiring a Doucoure-type and pairing them with Gana as part of those twin CM/DMs is essential.  In that scenario, Gomes could play the same role as Gylfi - deeper sitting playmaker, but with VERY different effects.  I wonder if he had a bit more freedom whether or not he would create more.  Maybe.