The likes of Wilshere, Walker, Lukaku, Sturridge have benefited from stints at PL clubs so it can be used to accelerate a player's development. We have only ourselves to blame if we don't make use of the system. Do agree the on-loan player should be allowed to play against his parent club though.
Besides, Chelsea will continue to stockpile players whether they can loan them out to a PL club. Most of their loanees are in other leagues fwiw (La Liga, Serie A, Eredivisie).