Borthwick, so long on the fringes of the international team with his 24 caps spread over six years, finally appears to have established himself as a regular first choice and, as far as Grewcock is concerned, it is long overdue.
"Sometimes 'Borth' gets pigeon-holed as being a bit of a lineout forward and he's definitely very good at it but there's a lot more to him than that," British & Irish Lion Grewcock said.
"The rest of his game is incredibly strong now. He's a great thinker of the game but also somebody who works incredibly hard.
"Recently he has also proved what a good defender he is and a good mover.
"I feel it helps my game having Steve there, with the work he does in the lineout and in the loose.
"You know what each other are going to do and it makes communication a bit easier because you know what to expect.
"We have played at club level together for five years so that definitely helps."
Even though Scott Murray's suspension following his sending-off in the 28-18 defeat by Wales in Cardiff has cost Scotland their leading lineout jumper for Saturday's Murrayfield match, Grewcock does not believe it will make the task any easier for England.
"Scott Murray plays a massive part in the Scots' team. He's a world-class player, without a doubt, but, with him not being there, I imagine the forwards will raise their game.
"Scott is probably one of the first names to be written into the team so it gives another guy an opportunity to play in his jersey.
"They are still going to be a fantastic lineout, they have still got very good players there, they are playing at home and will have gained great confidence with their win against France, who were one of the tournament favourites."