Other than the things he lists (sports, wildlife, astronomy) where *would* you need a 1000mm lens? If the guy‘s a landscape photographer he doesn’t need it. If he shoots portraits he doesn’t need it. If he’s a street photographer he doesn’t need it. Wedding photographer: not useful. In fact, 1000mm would be useless in those situations.
Have you ever done any landscape photography? People stuck using wide lenses are missing out, between 200-600 and beyond is common. I know people that shoot the moon at like 1600mm if I remember correctly.
For landscapes I use a 100-400mm lens half the time, and used to use a 600 on a crop Canon which is 960mm all the time until it was stolen. Compression compression compression.