I am not sure exactly what causes this bug other than it seems to be correlated with having a lot of tabs open and loaded.
Steps to reproduce:
I opened the following pages in both Orion and Safari: (identifiers removed because that's my info)
classroom.google.com * 3
docs.google.com * 4
drive.google.com * 3
youtube.com * 4
sites.google.com * 3
In the end, Orion reached 6533 MB, Safari: 5333 MB. Measured by taking the child processes and adding them all up. If you include the parent, just add another 1700. Keep in mind that my computer only has 8GB of memory, so that measurement may be a bit wrong, but the proportion should be accurate. Orion uses 123% of Safari.
Orion does not lag out as much.
Orion and macOS:
Orion Version 0.99.108.1-beta (WebKit 613.1.10)
<- Orion (I think)
<- Safari (Most of it, the rest contains the full tab and I don't want that on the internet)