"One of the biggest mistakes players make is to devote massive amounts of time to openings. This is because openings tend to be very concrete, and beginners think that simply memorizing an opening will give them an unassailable advantage over their opponents6.
Don’t bother spending any time studying openings outside of analyzing your games. Just make sure you know the basic opening principles."
It's how a beginner becomes an intermediate player.
There are some lines that are useful to know (Avoid various <10 move mates, mostly), but beyond that basic principles will get you to 1800-2000, IF you have the tactics and calculation skills.
Plenty of examples in the high ranks too - notably Magnus Carlsen (World #1) spends very little time on openings compared to most 2600+ GMs.
Knowing the SCO took me from 800 to 1600.
Thats absolutely ridiculous and SCO is a poor reference anyway. There are a lot of good opening books that cover specific openings to ever rely on an a comprehensive guide anyway.
I'll a little confused that you claim to 'know' it. You reviewed the entire book even if you don't play certain openings or defenses? There is a lot better use of your time.
To be precise - "knowing the mainline of common and popular standard openings from the SCO..."
No it isn't. Having a good grasp of chess tactics makes you an intermediate player. So what if you memorize opening lines? Your intermediate opponent isn't going to follow them at all.