I think using private english certificate is good because it is more practical than current entrance exam. Japanese entrance exam needs some "exam skill" so I think spending time for getting such skill is waste of time.
Furthermore, English is just one of basic skills so if they pass certain level certificate, it is enough, I think.
I don't know why so-called japanese top level university is so keen to their entrance exam. Most important thing is that whether or not these university are attractive for really talented students. Their name brand is meaningless, I think.
If they are talent and boring school, they only choose high-levek university but if high-level university are stick to such "score that needs exam skill", these university is not attractive for talented student.
Japanese education system have a good aspect that public school's fee is not expensive so I hope there will be more school that is not required such a strange "exam skill" and where people can study high-level topics.