Eh, I did this commute for 3 years (2014-2017). The low end of those Google estimates are basically the drive times with no-traffic, under ideal conditions (basically, no weekday morning/evening ever). The high end is closer to the norm under normal circumstances. Add additional time for an accident, HOV lane breakdown, light rain, etc.
I agree that the SCR times are less than ideal and won't realistically attract new daily commuters. They're just too long. But I'd argue that the real world travel times probably compete with or beat real-world drive times for most Boston area commuters. Back Bay and Longwood are probably a quicker drive under most conditions since the transfer options are limited and slow. But Financial District, Government Center, Beacon Hill, North Station and just about anything in Cambridge/Somerville that's not immediately off of I-93 is probably better via the train. Even with a transfer.
I think Phase 1 is going to mostly improve travel comfort for people who are already making the commute. It'll also make visiting Boston easier for a day trip. If I still lived in the area, it would easily be my default mode of commuting now. But it's certainly not going to entice new Boston commuters to FR/NB.