Li's clearing of Milan's debts were paid for by Elliott, no? Or from the mysterious money he cobbled together, lost, and then faded away without fighting over millions?
I'm not sure it was easy, the increase in value was only possible because they had rapidly increased performances while cutting costs--a very difficult thing to do. It also was an undervalued asset, with a stone-age marketing department that did not leverage the strength of the brand.
Oaktree did not have to invest into Inter, they chose to do that, while Elliott chose the better brand to invest in.
The next jump in Milan's value will come with a stadium, and the real estate portfolio that a sports team allows you to acquire--like San Donato. San Donato allows you to sell Milanello, either to develop San Donato and the surrounding areas, or to utilize San Siro as the next stage of your portfolio growth. That's what Arsenal did with Highbury, what Chelsea wants to do (but can't because the fans have insane control over Stamford Bridge), it's the key to that next jump in valuation.
The other key jump would be to push Milan's sporting success to the next level, and that would require marketing expertise that Elliott does not have, sponsorship revenue and the reach of Milan, as a brand, is that second area, but it is only possible with the sporting side. I think Elliott thought they were handing over a solid sporting area that had to be maximized by Redbird with their marketing and media expertise.
I have become increasingly convinced that Elliott brought Redbird on as a partner to maximize those two areas, the stadium and brand leverage, and while they are still doing well with the stadium, they have failed so miserably at the sporting side of things that it is hurting the brand marketing work they are trying to do.