I've been looking at this too. There are a lot of old reviews on the Sony versions. In theory, this should be a good indicator of G1 and G2 differences, but we don't know if anything else changed.
I know YouTube reviewers are often not trusted, but I do think Dustin Abbott is credible. He gives a lot of good historic context, that the G1 was a very good lens being the #1 seller in the world for a time, and the G2 was even more outstanding.
Adrian Alford may not be known as a super technical reviewer, but his review said it was competitive with the 24-120, which is saying a lot.
Thom Hogan's reviews are extremely thorough and well written, so you might want to wait for that if you're on the fence. Also, the Tamron lenses seem to go on sale after being released, so you might want to wait if there is no immediate need.
For me, I've been looking at it as a replacement for the 24-120. The 24-120 is wider, but often not wide enough when I do city travel so I need to carry an ultrawide lens anyway. If you're stopping down, performance can be similar to the 24-200, which has a more common filter thread and more focal range. The 2.8 might be better for night photography, if the lens is sufficiently sharp. The max subject isolation for 75 F2.8 and 120 F4 might be negligible, but would be higher at the same focal lengths at 2.8. When you take photos in busy places with lots of tourists everywhere, subject isolation becomes very important to me.
