Well there's the other side... County sides are probably mixed between The Old Pros, the England Hopefuls, the promising players, Young'uns and overseas. Now the Hopefuls and the promising players will mostly benefit with and against Overseas players and will gain experience. Less overseas will probably mean more people coming in trying to qualify through residency which could wake the Promising and lagging players and get them to perform for their spot.
If a player is good enough they will make it. Im not quite sure how Clark will benefit greatly from bowling to fringe county players whereas those young guns, who are the future England players, can only benefit from facing the best bowlers in the world.
To put it bluntly Emburey is talking out of his bottom. IMO of course