As someone who owns a 8 year old laptop, which works flawlessly over W10 and is waiting to buy his first Mac (I don't really need it but for aesthetic and full compatibility with coworkers and clients) Things like that make me wonder ... WTF!
No... seriously... is that even normal on Mac OS X? Maybe you got virus (there are virus for mac), or you need to format your macbook (fresh install is good also on Macs for what I've read) or maybe the famous obsolescence from Apple is real, I don't know, but I refuse to belive that a few new software (system and apps) suddenly transform your 4 year old laptop maxed out into a potato.
Sorry but no, it can be like that. Someone please tell me that OS X doesn't work like that *cries in a corner.
No doubt a fresh install will help. I've never done a clean install on this machine as I'm too lazy to reinstall all my apps and settings. It's not sluggish that impacts my workflow. I just notice when I open a new tab that it can take a second to pop open instead of being instantaneous.