Many articles and videos are simply some one repeating what they saw or heard, right or wrong. Joining with a router table is much like hand nailing with nail gun nails. It can be done but is it the preferred or best way to do it?
Why does a jointer work better than using a router table to join boards?
To begin with "mass", the jointer is heavy and absorbs vibration and is typically all iron so that it does not flex. The router table is pretty much light weight by comparison and not as stiff.
When you are joining on a jointer you use the weight of the material to help hold the work against the cutter and indexing surfaces. Not to mention it is easier to push down vs. sideways like on a RT. And you can use your body weight to pus down on the work as it goes through a jointer. Your weight is not used to keep the work against the cutter on a router table.
One more thing on you technique that may not have been covered. When you are running the work on the RT are you straightening the convex edge of the board? If not you will be changing feed direction all through the cut if the fence on both sides is not as long as the work.