Harry and his supporters won’t see this, but the Taylor Swift example undermines Harry’s case, it doesn’t support it. It shows that the Met (who already have a separate division that is available to protect public figures other than royals and MPs - it protected Salman Rushdie and I’m guessing recently Holly Willoughby, for example) will provide security if their assessment of the level of threat justifies it. There was obviously a high threat level against Taylor - she had to cancel the tour leg immediately before she travelled to London. And while MPs may have been lobbying, we have no indication what tilted the scales with the Met - the potential threat is obvious though, even to plebs like us.
Harry has the same deal as Taylor - if there’s a serious threat, you’ll get security. So far presumably he’s not passed that threshold. Taylor did.