GSC 1v1 should absolutely be in OGPL.
Now Bandit already mentioned the player base, and I would like to follow up on that.
GSC Cup had 32 signups. Now this doesn't sound that impressive on paper, but GSC Cup was going on during Classic, and didn't have points going towards Classic. The fact that 32 people decided to sign up for a tour that didn't count for the big official tour that was going on, and spent time prepping for GSC instead of other gens, says something. The list of users that signed up also shows that it isn't a dead gen. A lot of these users are big 1v1 names, and while many of these may play another gen, it shows that GSC 1v1 has at least a decent player base.
I don't want to trash on DPP too hard, all I will say is that the playerbase is much smaller, and I believe that many people wouldn't want to play the slot if they were needed for it.
I believe the optimal slots are 2 SS, 2 SM, 1 ORAS, 1 BW, 1 ADV, and 1 GSC. I believe that the gen skip is made up for the quality of GSC over DPP. Saying 1 liners about how the gen is dogshit does not change that it has a solid player base, and it has a lot of support. If there was a nineth slot, I would 100% support DPP, but since we are limited to eight, GSC 1v1 should be in OGPL over DPP.