Its not the same.. Both players are very good and play the exact same position.
Chiesa starting would mean we would have a better start but then he will not have the effect he can add with his speed vs burn out guys
He did not have the effect last night with his speed, he did it with skill while scoring that goal. In fact towards the end he made some bad decisions on counters and lost a couple balls there. All I could think about is Allegri going mad on the sideline for not valuing the possessions there.
Anyway, this 'effect' is way overrated. We're talking about professional footballers who are all fit and could play for much longer if they had to. It is very rare that this kind of effect happens. Other team can also make subs and nullify that effect. Spinazzola was great early on when Austria defenders were not tired but as game went on they defended much better against him.
I get this kind of thinking with an inconsistent player like Costa was or even Cuadrado sometimes. But Chiesa plays the same way all the time, he is definitely a starter. He had 26 G/A in 39 starts last season.
And also, coming on as a sub gives you a little bit of an advantage physically but also a lot less time and more pressure to make instant impact.