Brand new PC, lag delay

Hello tech forum, having an issue with a new PC i purchased that is really weird to me. After buying a new pc i am getting weird packet loss (it seems like anyway) lag in FFXIV, people freezing in place and then executing all actions quickly to catch up, but ONLY when i open battle.net or league of legends client or any other game, (web browsers skype are fine).

Any 2 other games can be running and i get no lag whatsoever in either game and i also checked by loading up an actual game of League while FFXIV was running. no fps lag in either at all and my ping in league was normal at 80. Also my computer before this had no problem with this at all (on the same exact wire) and if other people on my network are gaming it doesn't effect it either. Its literally only FFXIV and only with another game open. So confused. I assume its something on my end, im just trying to figure out what it is. I also realize I could just play without any game or game client open, but i bought a new pc to handle things like this so i can chat with friends outside of FFXIV on my second screen. Thank you in advance for any assistance.

XIV is a resource hog...when it is in focus it will consume massive resources in a bad way. Other games will be far better optimized across multiple cores and play nicer with each other because if it.

Thanks for the reply, picked up an SSD and installed FF to that and it seems to be working well now.