Well, it should be faster. I'm not sure I trust GO though to remove the 5-minute padding at Union (it's a 7-minute lay-over now). This has only gotten longer in recent years. Nor do I trust them to not break the line into two at Union. Or finish speeding up the track speeds through Union.
And then there's the last mile situation. I'm just under a mile to the GO, and normally take the streetcar. But there's still a 3-4 minute walk to Danforth GO, which was poorly designed for transfers to other modes. Sure, it's (Google says) an extra 8 minutes to get to the Gerrard subway station - but the connection time should be much faster, and I don't trust GO to move Lakeshore to every 5-minute frequencies (over 40 years after they promised this) - especially on evenings and weekends, when I'm usually travelling. Or even fare integration.
But yeah, maybe it will be faster, or at least similar. And on a nice day, I can at least walk to Danforth.
It depends what you count. There's been closures on Adelaide while they've been building the detour streetcar track, so they can close Queen Street.