My thoughts are simply this - City are well on course to win the PL with a points total never before reached in history across ANY of Europe's top 5 leagues. More than either of Barcelona or Real Madrid at their respective peaks have managed. More than Juventus when they used to completely dominate Serie A. More than Bayern have ever managed in their 'one-team league', more than PSG have managed in recent seasons, more than Mourinho's big-spending Chelsea of over a decade ago.
To compare yourselves to them at this moment in time is absurd, they are well ahead of the chasing pack and that is not down to Mourinho. You could have brought SAF back at the start of this season and it would make no difference, they are simply performing on an unseen level at the moment.
United themselves are as good as any other team in the PL right now outside of City, that is something I can say confidently and that was simply not the case 18 months ago before Mourinho came in. If the board are happy with that and the progress that's being made fine, if they want to see quicker progress and United close the gap on City in the short-term then they need to spend more, it's as simple as that. Money is everything in football, Mourinho has basically come out and said this has been known since he himself took over Chelsea and 'bought' the PL title in 04-05.
City had a much better squad than United when both Pep & Jose were appointed AND they've spent more money, he is one of the best manager's of the modern era but he is not a miracle worker. Even SAF came up against some formidable challengers in his time at United that he couldn't compete with - Mourinho's early Chelsea side & Arsenal's Invincibles for example. It might hurt to read, but unfortunately this City side right now are a team of that ilk who are historically good.
Competing with a side that good is difficult enough, trying to do it in the short-term when you've taken charge of a club after several seasons of transitional turmoil whilst spending LESS than said side is completely unrealistic. United fans should be thankful they have someone like Mourinho in charge, he is a born-winner with an extraordinary will to win, how many other managers in his comfortable position - and let's be honest, it is comfortable as you're 2nd in the league, easily through to the CL knock-out rounds, and he has 2 trophies in the bank from last year - would speak out against the club's board in an attempt to support the club's interests? He is saying it like it is and arguably putting himself in an uncomfortable position because he wants United to be better just as all the fans do.