The problem is that what you say is true, but in practice unworkable.Doing it properly is the key!
By notification and documentation of correct procedures, that will go a long way to proving the correct methods have been used, if not, then you should be made accountable.
As I see it, there are three main groups of DIYers (the boundaries are quite blurred though).
You've one group that is capable and knowledgable to do a decent job. All "Part P" did was **** them off, make them resent the rules in general, and/or make them into criminals.
You've a large group in the middle who know their limitations. If in doubt they'd ask.
But, you've now made it so that asking is tantamount to admitting in public that you're doing something illegal. So a large section of those will now go ahead without asking. Good safety policy - encourage people to now ask for help
And then there are those that will have carried on regardless, don't care what the law says (even if they know), and nothing will catch them (in practical terms).
So of those 3 groups, the main target was the last group - who really haven't been that much affected. The first two effectively get punished for the failings of others. IMO I believe the legislators have perhaps heard enough complaints to realise that what we currently have is counterproductive and so are relaxing the rules.
And of course, we all know that "Part P" has been a licence for the unscrupulous to squeeze money out of frightened grannies ...