Can concur. I bought a plugin a few years ago after using the free version for many years, wanting to support the devs for making such a useful plugin. I installed it on a few sites, and left my PC running overnight with a tab open to the plugin and woke up the next day to a lovely rebooted Windows (I hate how default Windows behavior after BSOD is a reboot with ZERO indication that it crashed or if it was an update that rebooted). Re-opened all my tabs, and queue the same waking up the next day to a freshly rebooted Windows, which made me suspicious. I assumed at that point it must have been a BSOD, so dug into Windows event logs, eventually realizing it was Firefox. Restored tabs yet again, left browser open over night, while installing more and more debugging tools for Firefox, none of which helped me track down the culprit. What pissed me off the most was that Firefox even allowed a process to consume > 30GB of RAM and cause my PC to crash! I finally caught it one night after > 10 BSODs - the tab had been open for 20+ hours, and right as it started to spiral out of control and my PC was about to crash, as programs were starting to error out and Windows was madly paging things to disk. I got lucky, and was able to open about:memory to see the culprit - this plugin had some kind of memory leak that wasn't noticeable but then suddenly went nuts. I emailed the devs multiple times with the full debug output, and was ignored for weeks until finally they responded, which pissed me off even more having finally paid for the pro version, only to be greeted with this. The free version didn't seem to have this issue either, which was like an extra slap in the face.

Naked Wordpress is plenty fast, but as soon as you start adding sketchy plugins and Themes, things can spiral out of control.