For comparison, There's two garphics card, they're both the same and they're both built with the same gpu architecture and same model type.. Lets compare two GTX 680 they are both identical but one of the video cards has 4gb GDDR5 of ram and the other has 2gb GDDR5 of ram, which one will perform better? they both can run the same game, they both can do 1080p up to 1600p . Now this what the extra 2gb of memory execel from, it can handle multi monitors better, it handles higher resolution better before it runs out of memory, it renders stuff faster.
The HD 7770 equivalent thats in the XBOne is a low end card, to make that low end card worse, it has ddr3 memory, DDR3 memory its old and slow for todays GPU standards, at least they should've kept with GDDR5 memory for the GPU and ddr3 for system memory. Xbox one gpu will struggle to render stuff fast enough at higher settings and at higher resolutions mostly due to its slower memory .. Devs really would have to optimize their multi plat games made for the XBone just to keep the same quality on both platforms.
The HD 7870 equivalent in the PS4 is a mid range card with GDDR5 memory, this card is pretty beefy, it can handle higher res without sacrificing fps, it will render stuff faster due to the faster memory, games will run smooth on both platform but that same game will run smoother on the PS4 with less sacrifices ..
In short, Xbone multi plat games = harder to program for due to the slower gpu and slower memory which leads to more time consuming due to the optimization (sacrificing) issues just to keep quality on par with the PS4.
PS4 multi plat games = easier to program for due to its faster gpu and memory ( no need to cut corners) and less time consuming, more straight foward, less sacrifices .
Even though multi plat games will be on par on both system, the XBONE version will take extra time (optimization) to equaly match the same game on the PS4 ... The extra power and ease to program for would make the PS4 the lead platform.. IMO.