It's not about that though, it's about a top prospect like Perez wanting game time every week. He's not going to be too happy sitting on the bench at a relegation struggler. He could do that at Spurs and be playing Champions League football and seeing more game time due to volume of games.
Fair enough, if it's Anita or Colback, but not someone with Perez's ability.
What if Perez is injured or out of form? What if Berahino is injured or out of form? What if we play 442 with Perez playing with Berahino?