PS4 alone sold almost 100 million units until last December. Every multi platform AAA game sells more on PS4 than on any other Platform. Even witcher 3, wich was a big hit on PC, still sold more on Console:
https://www.dualshockers.com/witcher-sales-ps4-xbox-one-pc/
I see almost every AAA multi platform game "dead" on Steam Stats. There are few exceptions. Looking at top 30 played games on Steam, it is hard to find AAA multiplatform games. F1 is empty, PES is empty, Street Fighter is empty, Tekken is empty, Mortal Kombat is empty, etc etc
Idk what makes you think Borderlands would have more sells on PC than console, but let me get this straight: It won´t, just like no multiplatform game does.
Now, if you want to talk how PC is the biggest market? Maybe, because it has titles like League of Legends, Dota, Heartstone, WoW and other e-sports titles that are played by millions of people. Also while everyone in 2019 has a PC for daily workflow, not everyone has a dedicated gaming system (console). People with PCs to do their daily stuff, also play games sometimes. FML even my mom has steam installed to play some random puzzle game she loves.
But remember PS4 has 100 million users too. And the 3rd party multiplatform games are defo most played on console, not PC.