I understand that. If losing a relegation series without demoting is equivalent to "demoting" and "bot promoting" then you'll have 2 effects conflicting: the demotion and the bot promotion (it's a fair assumption that if one is taken into account, also the other is). The end result is difficult to quantify, but I agree that you probably lose some revenues the following season. However since you can also build seats (if you're not capped) or generate profits with the extra revenues that should absorb some of the potential losses.
The main point is the significant difference in bot promotion and promotion via winning the title. From the game manual:
Both promoting league champions and teams that promoted from a bot cleanup will get the extra cash, though bot-promoted teams will not experience the same boost to their season ticket holders.
So the distinction there is that if relegation from the lowest active series counts as a relegation and bot promotion, it's very harmful to a team's season ticket holder base. It very well may not process that way, of course, and it may not be entirely relevant to this specific user, but it's the sort of thing that one would definitely want to be aware of and try to find good data on if they're in this scenario.