I watched a benchmark of the rise of the tomb raider the other day with a phenom ii 965 and a 1050ti and the cpu stayed below 90% the whole time. Sometimes as low as 78%...
The gpu was maxed the whole time at 99%/100%
It depends on the game... Some are more gpu intensive others are more cpu intensive, but the point being in this case the 1050ti bottle necked the phenom as the phenom still had quite abit of headroom to play with at points.
Having said this... Most AM3 boards support pci-e 2 and so are not making the most of the 1050ti which is pci-e 3 (I think) compatable. So maybe this could be the reason for the results above, meaning that the combo of mobo and cpu are bottlenecking the gpu... so in essence yes the cpu could be... but this is all theoretical
Check what games you want to play... See if they tend to be more cpu or gpu intensive. But tbf at 1080p high (not ultra) settings, you should get very playable framerates with a phenom ii... For now.
You have probably already made up you mind and purchased by now but for others still considering this, it's something to think about.