I managed to get the sin to win on the xbox version, so atleast the achievement pops.
Just very hard to get, its still 3 high tackles in 1 half to get yellow card (Or was before wednesday update, who knows now, as ive not seen a single high tackle).
In update 17 i realised you could short box kick over ruck to make opposition 9 run back slightly, then sprint in to them and tackle and seemed to force same high tackle penalty that blitz defence tactic used to.
I also think when you have a yellow card the AI defence ramps up for some reason, took me the full 10 minutes of my yellow card to get the try, because the AI became unrelenting and seemed to win constant turnovers even as a lower rated team. 
800 tackles worked for me on PC, but not Xbox, so not sure what that issue it. Achievement potential seems to change depending on patch and platform.