It allows another player to get to marker, it doesnt have to be the tackler.
I think you are confusing what you think is legs tacklers holding on longer with tacklers lying around in the play the ball getting in the dummy halfs way, which has clearly become a tactic…refs are instructed not to penalise this as it just makes the ruck messier as is
But that already exists. Any two players can stand at marker if the legs tackler rolls away and retreats to the line. Not saying anything about tacklers generally lying around.
**What I am saying is regardless of how long you let a clean 1-1 legs tackler hold on, he is going to struggle to get to his feet and back to marker more quickly than the attacker to his feet and playing the ball. Therefore really all the ref needs to do is allow the legs tackler to hold on a bit longer to let the markers set, which has already been implemented this year as a sort of variation on dominant tackles.**