You'd be surprised how good Pjanic fares compared to Pogba and Marchiso.
G&A
Pogba: 8 G and 12 A in 3019 min.
Pjanic: 10 G and 12 A in 2654 min.
Marchisio: 0 G and 2 A in 1931 min.
Passing
Pogba: 48.5 passes/game, 83.4% success rate, 1.5 keypasses/game.
Pjanic:
65.5 passes/game (beast), 84.9% success rate,
2.4 keypasses/game (beast).
March: 63.5 passes/game,
88.5% success rate (beast), 1 key passes/game (God I miss Pirlo).
EDIT: For my own entertainment. Pirlo's last season with us passing stats.
Pirlo 2014/15: 72.7 passes/game (God), 89.2% success rate (God), 2.2 key passes/game. They said Pirlo had no role in our last season
Pirlo 2011/12: 86.4 passes/game (God is his bitch), 92.9% success rate (God is his bitch), 3.4 key passes/game (God is his bitch). Best passer of all time easily.
Defense
Pogba:
2.2 tackles/game (beast), 1.3 Interceptions/game,
dribbled past him 0.7/game (beast)
Pjanic: 1.4 tackles/game, 1.5 interceptions/game, dribbled past him 1.4/game
March: 2.1 tackles/game,
2.8 interceptions/game, dribbled past him 1.3/game
So this is a guy whose numbers are excellent. He is more creative than Pogba, he is at the heart of everything Roma does offensively, is great in possession and defensively is not too bad. Even his average rating on Who scored is between Pogba's and Marchisio's both of which are consistently good players.
Pogba and Marchisio are top level players and so is Pjanic. Gomes (based on just stats) is a level below them.