Bottleneck calculators are totally useless in my opinion.
It depends on the game in some very cpu heavy games at 1080p it may hold back a 2070 a bit, though im sure anything currently out will still run very well regardless of if there is a slight cpu bottleneck. At 1440p I doubt there will be any cpu bottleneck at all in current games.
I hope the person you are gifting your GTX 1070 will put it to good use. Otherwise, that would be an expensive upgrade for a relatively small jump in performance. RTX 2070 is on par with a GTX 1080. I would only do that if they main reason for the upgrade was to gift the GTX 1070.
Many folks seemed certain the difference between AMD and INtel is but 5-10%, and, when confronted with CPU comparisons using top GPUs show the difference can be 30+%, folks then complain ad nauseam that 'the settings were not high enough to shift the load mostly to the GPU', etc...
The R5-1600 gives 'good performance, but, it would be hard to deny that in some games at even 1440P, it might be down some 30%...; will this matter if getting 100 fps on a 60 Hz monitor? No. WIll it matter when trying to achieve 144 FPS minimums for a 144 Hz monitor? It sure might.
Pairing a 9900K with a GTX1050 seems odd, as would pairing an R3-1200 with an RTX2080Ti....; most rigs are well in between of either, with lesser degrees of 'oddness', and, all opinions are only that.