It was in a much worse state 20 years ago than Old Trafford is now. That’s one of the better Italian stadiums too.
There’s far bigger issues.
I think you make a good point, and it is always important to see the whole picture when analyzing a situation.
The narrative is that the club 'must' do this and that. In reality it is a bit more complex. What is abundantly clear is that we are:
(a) Not setting aside any funds to improve the infrastructure.
(b) Not paying off our debt, that is significant, instead its increasing.
(c) We do not have any margins to do the above, we would have to do "a Tottenham" or "a Leicester" to have any chance to spend on the infrastructure
(d) We are a club that benefits greatly from being really big, the others can only compete with our profits if they win the PL/CL while we struggle. But this won't last forever. We are big because we were great. Kids of today don't nearly become United fans to the same extent. If we take 10 years to get the club in order, we would rob Peter to pay Paul, lose commercial incomes from our market position to gain incomes from the infrastructure.
We cannot keep running this club without being able to set aside funds for -- large -- investments in the infrastructure. Even if OT and Carrington could probably be used for another 10 years, there is definitely an underlying problem that is unsustainable. In addition, improving these things will probably be beneficial to do, sooner rather than later.
Lastly, like we are seeing from Chelsea and Manchester City -- it is absolutely crucial to have a youth academy that produces sellable players on a regular basis to compete at the highest level. To get there, it also requires investments that we cannot afford. If you buy kids for 45m every summer, it will pay off. We did it for a while under Solskjaer, but at other times we do nothing becuase we don't have the transfer funds.