It is remarkable how much the Queen's standing has improved during the time since that song (1977). My (UK) family are (as far as I know) staunch republicans, but the last couple of decades have seen all of us soften our disgust with the monarchy as Elizabeth represented it. We might still want the whole concept destroyed, but there is nothing close to the vehemence of Johnny Rotten (Lydon)'s lyrics from that song.
Nevertheless, that is how a bunch of people felt in 1977, and as our memories become even more gilded and rose goggled now that she has died, it may be worth remembering those feelings too:
God save the queen / The fascist regime / They made you a moron / A potential H bomb / God save the queen / She's not a human being / and There's no future / And England's dreaming
These days, I think even us staunch republicans/anti-monarchists would begrudgingly admit that "She could have been worse" and that she actually was a human being.
Maybe Charles will have the guts to end it all, but it doesn't seem likely.
One clear advantage of monarchs that I can see, are that they have an incentive to grow and expand their tax base. That typically means long-term planning (but doesn't ensure it, which is a disadvantage the UK parliamentary system seems to mitigate).
They are given a lot of money.
They can (and regularly do) veto legislation if it would harm their (vast) business empire.
They are not elected.
The burden of proof is on you to say why this is a good institution.