I had a G3 for one year, and I upgraded to a Digital Rebel in January.
As much as I liked my upgrade from an S30 to the G3, I like the upgrade to the Rebel even more!
I was amazed at how much faster the Rebel is at focusing than the G3.
In addition there is virtually no shutter lag with these DSLR's.
I can focus in almost complete darkness, especially since the Rebel uses the focus assist lamp on the external flashes (and the internal one is very powerful too), something the G3 couldnt do (I dont think the Pro1 will either).
Plus, the noise at ISO800 on the Rebel is lower than ISO100 on the G3.
Have a look at this thread:
https://photography-on-the.net/forum/showthread.php?t=33543
Take a look at the last 4 pictures all taken at ISO800. They are silky smooth!
In addition, if you like night photography, the Rebel has unlimited exposure time with the BULB setting, unlike the 15 sec limit of the G3.
Plus, the Rebel does noise reduction on the fly, so no waiting for the camera to take a second noise reduction shot like the G3.
I've taken 30 second exposures on my Rebel that were clearer (silky smooth) than 1/1000 shots on the G3.
With the Pro1 you will get shutter lag, more noise than even with the G3, slower focusing than a DSLR.
Oh, and did I mention all the len$es!
AFAIK, The Rebel has many more features than the G3 and Pro1, with one exception... Flash Exposure Compensation.
Everybody is different, but personally I couldnt bare going back to a point and shoot camera after using the Rebel.
That's just my experience. 
EOS R6 Mark II - Sigma 50/1.4 Art - Sigma 14-24/2.8 Art - Canon EF 70-200/2.8L Mark III - Godox Xpro-C - Godox TT685C x2