If it were me, I'd just upgrade to a i7 and keep the Motherboard and the RAM.
The games you have listed that Core i5 is plenty for, however if your looking for better performance the Core i7 is better. The GTX 1050 Ti is an ok video card, but with your current build I feel you could get far better performance with your budget if you kept that motherboard and invested into a good used Core i7 CPU and sold that GTX 1050 Ti and got something like a GTX 1660 as linked below and benchmark comparison below that.
If you wanted to you could even go more heavily into an even higher end video card and the Core i5 would still be plenty if you skip on the Core i7 upgrade. Additionally if your motherboard has room for additional RAM you could upgrade to 16GB.
GTX 1660
https://www.newegg.com/Product/Product.aspx?Item=N82E16814932130Benchmark Comparison
https://gpu.userbenchmark.com/Compare/Nvidia-GTX-1660-Ti-vs-Nvidia-GTX-1050/4037vs3650Lastly not sure if your system has any SSD drives in it or not, but my gaming systems all now have SSD drives for fast load times and minimal lag. I play all the games you list except for Starcraft 2 and have had awesome performance with an older system with modern higher end video card and two SSD drives.
My fastest system I have is a AMD FX-8350 4.0Ghz 8-core with 16GB DDR3 1600Mhz RAM and a GTX 780 Ti video card with two SSD's a Intel S545 256GB and a OCZ 90GB. I have my OS of Windows 10 on the 90GB SSD and the large install games on the Intel 256GB SSD. Performance is fast and no need for anything better for myself yet.
One test I did a while back was to take my 10 year old computer and install the GTX 780 Ti into that system and see if it made any difference or not. The computer an AMD Athlon II x4 620 2.6Ghz Quadcore with 8GB DDR2-800Mhz RAM and a Crucial 240GB SSD with this EVGA GTX 780 Ti video card in place of the GTX 260 I had in it prior, and I was very impressed with the fact that all games except for Witcher 3 ran flawless on this system with its 10 year old CPU, Motherboard, and RAM. The issue with Witcher 3 is that the game is CPU intensive, whereas all the other titles rely heavily on the GPU and so a 10 year old CPU made little difference. Witcher 3 does run on this Athlon II x4 620 2.6Ghz but all cores were hovering 90-100% CPU utilization and in events in the game that a lot was going on it would occasionally lag for a fraction of a second and it was all due to the CPU being flooded with data to crunch through for the game.
World of Warcraft, Diablo 3 and other games ran the same between the 10 year old computer and the new 8-core; but the CPU was quite busy on the 10 year old CPU whereas the new 8-core was just over an idle running the games.
So just wanted to run by you the possibility of stretching the life of what you already own and invest the money into what is causing you displeasure with performance which I feel is most likely the GTX 1050 Ti and could also be lag your seeing if your using Hard Drive(s) instead of SSD(s). RAM increased from 8GB to 16GB can help as well since your gaming and might also be multitasking with it such as dual display and game on one display and other stuff running on the other as I do. The Core i5 you have is pretty good for the games you have listed and a used good Core i7 could give you greater performance for games that need more CPU vs GPU.
My thoughts are that if you take that GTX 1050 Ti and put it into a newer build where CPU/Motherboard/RAM are only upgraded the performance increase is not going to be as good as you expect it to be.
I bought a GTX 1050 Ti and returned it for 2 reasons. #1 it had no legacy support for DVI-VGA for my second monitor as well as #2 there was no noticeable performance gain from the GTX 1050Ti from the GTX 780 Ti I had been running. It felt as if actually the GTX 1050 Ti was performing worse than the GTX 780 Ti, so I returned it to the store where I got it and got a full refund. The GTX1050 Ti to me feels almost like a GT card with GTX naming.
