What precisely is the difference between whataboutism and wanting people to live up to their own standards? How can you discourage hypocrisy without looking like you want to shift topics? Is character critique (which "you are a hypocrite" obviously is) even possible to do these days? How do we learn, if it isn't possible to encourage people towards the virtues they desire?
I think the issue is, when we think about hypocrites, it's usually public figures, particularly politicians. We don't know them. Trying to help someone be a good person only works if you're close, they trust you, and you have any chance at all to impact them and their life.
So instead of shaming politicians, it's better to make the point that the true audience for that comment ought to hear: this person will say anything, and you should routinely ignore what they say, because it doesn't seem to matter. This framing makes it clear that someone being convinced and changing their mind isn't a problem – it's just if someone starts making promises, or provides flimsy reasoning about why they disagree with their previous view.
I think it's compassionate to want people to live up to their own standards, and probably still quite good to want them to live up to your own. But public figures exist in parasocial relationships. We don't know them. Let's stop acting like we are buddies, or out for their best interest.
I think this is why discussion podcasts can have such a useful tone – if someone is behaving this way, you can chastise the person you know and care about in front of the audience. We all have something valuable to contribute, and we all goof. Let people hear it, let them hear what someone might say to someone they care about, and let them extend that empathy into their own heart, if they can.
But let's not kid ourselves: the politicians don't trust us enough to take our advice. They don't trust us at all. How could they?