The spare stuff is annoying because the Andrew is such a disaster, and Harry has made it his life's work now to paint being the next in line to the heir as such a burden. (And the Crown hyped up Margaret's off the rail moments)
Plus Diana and her "I wasn't needed anymore once I'd provided an heir and A spare"
It's made it seem to some people as though there is only one spare and that role creates an burden or a corrupting influence.
All the siblings to the King are 'spares' until the heir has kids, because you never know what's going to happen. So imo Anne and Edward were both spares alongside Andrew.
I do think it's a good thing to have more than one sibling to the heir to make it feel less of a contrast between siblings though.
Andrew was only 22 when William was born - he could technically still have been needed for the line of succession but Charles' siblings effectively stopped being spares at that point.
I also thought Harry's comment that he only had a limited time to make his mark before all the attention would be on George was telling. George growing up doesn't stop Harry doing good work, he's not talking about the work, he's talking about press attention, which tells you that he cares more about how he's perceived than doing something for its own sake.