They call held when in their opinion, the tackle is completed

Gosh

I lost track of the number of times a Leeds player(s) pulled the Cas man to the ground once the ref had called held...

Isn't it also called held if another attacker gets involved and pushes the ball carrier forward? In order to stop it turning into a Union maul.

Yep.

They seem to be calling held a lot earlier this season whilst there is still momentum from the attacker, or from the defenders

New directives brought about due to increased use of illegal and dangerous tackling techniques advised that refs call "held" earlier. You can't really blame the refs - this will have been discussed between the MO Dept and the SL coaches. If coaches want to change back, stop coaching and/or condoning tackles targetting the knees.

It strikes me sometimes that ref's issue too many instructions to the players on an ongoing basis; the latest one seems to be the mini-coaching session that they hold around every scrum, which appears to be this years early rounds obsession. Form it, put the ball in and if players transgress, penalise them - too easy?

And on the run. One I've noticed so far this season is a continual instruction to "Play the ball on the mark" after the tackled player magically ends up 2/3 metres (or more) forward from where he was tackled in order to play the ball. Quite simply, if a player has moved forward that much to play the ball, it should be a penalty.

If you ping players for stepping off the mark all the time (& any other transgressions) they'll stop doing it, thus the ref wont have to keep blowing. of course a certain amount of latitude has to be shown but I'd far rather have enforcement to get the game cleaner than see all the messing about that we've had for years.