I had a similar experience yesterday.
I was rolling with a teammate that I believe I am more skilled compared to him, yet he outweighed me by around 25 pounds. I was trying an open guard sweep but couldn't pull it off on him and no matter how much I turned to my side in half guard, I always get flattened out. I also got tapped by a simple forearm choke, which I could normally defend.
Its true, sometimes if a guy is just stronger than you he can outmuscle you, the only thing left to do is to outthink the person or beat him to a move by 2 steps.
But, as one of my teammates said, if you wanna get better, its always good that you spar with guys who are very strong, and then mix it up with guys who are really technical. that way, you learn to adjust against different opponents