As powerful as Thanos is, with or without the Infinity Stones, he is simply another being who abides by the rules of the universe.
If he wanted to, he could erase Thanos, the Infinity Gauntlet, any and all of the Infinity Stones.
Thanos having all six Infinity Stones would only make Saitama that much more powerful than him, quite possibly making him the strongest person in the universe.