Ministerial instructions, in my view, are a very powerful instrument of government. They're very fast. My assumption is that the reason for this bill is that the minister has been unwilling or unable to issue a ministerial instruction. If the minister were willing to, then that's a very fast and easy way to make changes.
Having said that, one thing the bill does that ministerial instruction doesn't do is it ties the hands of future ministers. If the goal of the committee and Parliament is to tie the hands of the ministers, then you need legislation. There are advantages to tying the minister's hands, and there are advantages to giving the minister discretion. It depends on how much you trust and agree with the minister, and all future ministers.