>>63814818 (OP)No. It might have gotten them surprise and some kind of limited gains depending on how it was used, but NO weapon is a "war-winning" weapon on its own, because people will always develop countermeasures.
In this case, the Western Allies already had both protective gear and their own chemical weapons ready to go if it was used. (see Bari port bombing in Italy, 1944)
The Soviet might have taken some serious casualties, but they always do anyway, then they'd either issue their own masks/etc and shoot their own wargas, or the Western Allies would supply them with via Lend Lease.
Gas would just make everything more miserable than it already was.