You're right it does seem high. Tried to find out a bit more about this. In the Premiership 8 out of a squad of 25 must be home grown, so that's 32% (around a third) but I suppose that could be a mixture of British players so need to drill down a bit more to find the percentage of English players. Also being in the squad doesn't mean the players are necessarily playing regularly.
The foreign player percentage seems to be around 70% so clubs are definitely maxing out on their allocation rather than investing in home grown talent. Seems a shame that short term fix trumps long term potential especially when you think of the millions spent on players and agents.