If both hands are touching the ball, it's catchable and the WR needs to adjust their body and movement in order to secure the ball. Lassiter has had several catchable balls that he has dropped. He may not have picked up yards after catch if he caught the ball, but he still could have caught it. Lassiter is playing for YAC, which is great and all... but not every pass is going to produce YAC. So if he is dropping passing that would result in a 5 to 8 yard gain with no YAC, that's a problem because he is playing for himself and not adjusting to the ball... he wants the ball to adjust to him.
Lassiter needs to stop with the talk if he can't back up every pass thrown to him and is catchable, with a catch. His YAC are great... really good, and he could have more of those opportunities if he catches the passes that would require him to go to the ground for or make the necessary adjustments to the ball that would take him out of position to YAC.