Most teams have about 20% turnover year over year, or about 10 players who would be newcomers. Some of the better teams have less turnover, and some of the lesser teams have more.
The Dolphins from a couple of years ago (under the Wa-NICK-er) had somewhere closer to 35% turnover, which was rather a lot.
...but this year's team will exceed that. 47 of the 80 players are newcomers. Meaning that even if all 33 of the players who were around last year made the team there were be ~40% turnover.
And you know that not all 33 will make the team. Some are fringe players, some will be pushed by a newcomer. So, it could be as high as 50% turnover if 6 guys don't make it...
(btw, I don't have much info on the 69-70 transition, but I have to figure it was around 30%)