I think Rhino's troubles are a technique thing. Using Liam Fulton and Ellis as the comparison- you see those 2 guys run between tacklers far more the Heighington, who seems to aim up right at the tackler. For 'smaller' guys like Fulton, hitting the gap between tacklers, at pace, is what makes them effective. If Fulton ran AT defenders, he'd be ineffective. Guys like Ellis, who are physically big & powerful, can run AT defenders & be effective. Heighington is neither 'big' or 'powerful'. He'd be much better advised attacking the gaps at pace, than hitting the line with that shuffle he uses.
That said, it's VERY hard to complain about a guy that obviously puts in 100% every game. In fact, his on field demeanour & attitude may be more important to the team than his actual play.
I reckon you find a spot for him every week & live with whatever deficiancies he brings, because you know, when the game is on the line & THAT tackle needs to be made- he'll have his hand up.
