I think it's more in the lines of:
1) steam
2) battlenet
3) origin
4) uplay
5) gog

Keep in mind that Ubisoft games sold on steam require Uplay. EA hasn't sold anything newer than 2010 on anything else except Origin. Blizzard has never sold anything anywhere else until Diablo. Also Epic store is gaining traction quickly, all those freebies and exclusives might already have managed to get enough people to surpass GOG.

I suppose as long as people believe Steam = PC gaming, GOG will always have a tough time attracting any form of attention.

I can understand this from the other perspective: I only care about DRM-free gaming, so I'm never going to log onto the Steam or Epic etc. platforms in the first place, so I'll never know nor care about whatever it is that they're selling over there.

I like the client-free model, and I am not interested in having a 3rd party snooping around in my PC watching what games I play or gathering stats about how I play or who knows what else...

GOG should stay drm free. I'm not installing what's basically a rootkit just to play a game. No way,

I think the true root of the problem lies in that GOG isn't very good at securing good games and has a tendency to cripple their relationships with other companies. There are many good games out there that haven't gotten much or any time in the limelight.

For example, One Finger Death Punch 2 has been released today. Not on GOG, and the original game isn't present either. Super Meat Boy was deliberately avoided by GOG because it already made a lot of sales on Steam - as a byproduct, preventing the opportunity to host Binding of Isaac and future games by the developer. GOG also turned down working with Cave/Degica. That lost a sizable catalog, possibly including A-Train and the RPGMaker tools.

GOG should be expanding the catalog, deliberately aiming for "A" and "B" grade material. The focus of Steam and Epic is on the AAA market, which leaves a niche that GOG could fill.

One Finger Death Punch 2

Lobotomy Corporation

Wild Guns Remastered

Musihimesama trailer

Earth Defense Force 4.1

Ace Attorney Trilogy

I think their DRM free requirement limits the AAA releases they can get day one, which in turn limits their user base, which in turn limits how persuasive their DRM argument is. It's a circle.

Also Steam is so entrenched it takes exclusives to make people look elsewhere, which is why that's what Epic is focusing on.