Paul Tassi who does articles for Forbes posted that 0.6% of all destiny players have Vex. If you count a player as “active” and someone with one seal then it is 1.6% have it. I’ve done 26 clears. If each person had not done the raid that week then there were 156 chances for vex to drop. I’ve only seen it drop 3 times. That drop rate 1.92% which is close to the 1.6% ownership rate. That’s 1/50 chance for a desired exotic that will likely only be “good” for a limited time.