regardless of berna, different positions require different skills. ronaldo would be an awful defender, de ligt would suck as a striker. matuidi is useful at a position that requires less running with the ball, he'd suck at the heart of any midfield when plenty of movement with the ball is required. bentancur is good on the ball, can tackle, but isn't fast enough for a winger. dybala isn't fast enough for a winger either, and as the closest he plays to the opposition goal, the better he can use his left foot.
yeah, it's nice to have versatile players with multiple skills. caceres was our wildcard player for years as he could cover multiple positions. vidal was a world class b2b mid and wasn't lost behind the strikers either. or an attacker that can defend both set pieces and in open play can save your ass when your defense is shaky.
it doesn't mean that any player should be able to adapt though. on paper, bonucci would make a decent regista with his passing, still, no coach had the nerves to try him before the defense yet. barzagli, one of the most reliable centre backs sucked ass as a right back. same for chiellini: his career basically started when he was moved to the centre from the left side of the backline. dybala sucked as a hybrid mid/winger last season, partly because of his poor form and approach, partly because of his tasks that he couldn't handle.
berna is in poor form and should absolutely be benched asap anyway, but he's not a trequartista.