Yeah a lot of ‘slashers’ aren’t really slashers are they. Just a convenient pigeon hole a lot of the time. A film like SWEET SIXTEEN falls under slasher but isn’t really. It’s not just about victims being slashed, it’s a whole vibe / style… I have not heard of DELUSION though
There's also Road Games (1981). If I'm not mistaken, this is the original Australian poster art
and I think this is the US poster art
the US poster gives off somewhat slasher vibes, and it has Jamie Lee Curtis in it, but Road Games is not a slasher.
Back in video rental days my mother and me rented everything that looked remotely like horror. Delusion was in the horror section and of course we rented and watched it, but it is not really horror except for a few corpses popping up in the final act. If anything, Delusion is an obscure one.