The offence of Misconduct in Public Office, as the name suggests, applies only to those in public office. So it's not a higher standard - it's another, different standard. You or I couldn't be prosecuted for the offence (assuming you don't hold a public office...).
I don't get it. You or I can't be prosecuted under it because we're not in public office, but people in public office can be prosecuted under it, thus there's a class of people held to higher standards.
There's a bunch of stuff that you and I can do, but that we couldn't do if we were in public office.
Members of the public are expected to meet one standard. There are additional -higher- standards placed upon people in public office.
I don't understand how a law that applies to a certain class of people, but not everybody, is not treating that certain class of people differently.
The law creates the higher standard. Behaviour that's perfectly legal for most people becomes illegal for people in public office because we expect higher standards from those people and we expect these higher standards so strongly we created a law to enforce it.