For the relation to the public. It's harder to take an event seriously when the same guy wins everything. Compare to the clay events in tennis when Nadal was at his most dominant - that was consistently the least popular part of the men's season, and things devolved into publicity stunts like the Madrid organisers with their blue clay. Or compare where darts was when Phil Taylor won nine world titles in a row to where it is now. Or heck, go back a century in this sport to the time when the Giro organisers paid Alfredo Binda to not start the race because people didn't care for his domination anymore. Or compare the viewership figures for the 2024 and 2025 Giri. Perhaps with the exception of athletes who become global brands, the presence of big names doesn't help any sporting event as much as the absence of competition hinders it - and Pogacar is nowhere near that level of stardom.
I follow your reasoning, and mostly agree, yet I think there is a difference between a "one off domination event" (for this race) that would get some headlines outside the sport, and suffocating domination in specific popular events.
Overall of course good competitive racing is better to attract interested viewership of the people actually viewing already, in the case of a small event like TdR I honestly don't know what kind of specific PR sucess they'd need to get a sponsor again. So maybe a historic news wothy feat does a better job, in this instance, not in general, to promote it again. But maybe it would also backfire, I don't know. It's in the end an empirical question we won't find an answer to a priori, and probably not at all because he isn't going to win all of the stages anyway.
As a last question: don't you think it would be better to have him win all stages and get some extra attention, rather than have him win by 3 min and win say 4 stages? Because that would just be utter domination as well, but without any newsworthyness.