There's certainly no harm in it.The only real evidence that might identify an Arthur is buried underground and may never be discovered. Some people like to chase will o`wisps. Sometimes they`ll even cause a stir. What`s the harm. There will always be the Peter Grahams of this world to reel them back in.
If Arthur was real, then you might be right when you talk about evidence buried underground. But if he wasn't, we have created a 'god of the gaps' scenario in which the possibility that an inscribed stone lies undiscovered under the soil can never be entirely rejected.
If Arthur isn't real, then we are left with what we already have. The better news is that we have more than we sometimes think. There are enough references to Arthur in texts which arguably pre-date the Historia Brittonum to show how Arthur was though of. None of it supprts the notion of Arthur as the Saxon-bashing hero of Badon (which I know you don't argue for anyway), but taken together, it does suggest that the idea of Arthur as a matchless warrior of folklore was well established by the seventh century. It's not until the ninth century that we see him recast as a man of flesh and blood.