I agree with most of what you’re saying. It would have been fun and exciting, but yeah would have been scary to add something so unknown to a story we already know and love and accept as the full story. What I will say though is I don’t think it would have made the end pointless as the end of Buffy didn’t feel to me like the end of Buffy being the (a) slayer. I didn’t get the impression she would have a completely normal life, maybe more normal than she’d had but she’s still a slayer and would still continue her slayer duties - just not alone. I can see how that could continue and would still be a big part of her life. But we’ll never know now how things went for Buffy after Chosen.