@Fortitude
The contentious point is not that Casemiro is good or bad, no one can question his quality, he is arguably the best DM in the world in the past 4-5 years, he is only 30 years young, and still has at least another 4-5 great years to go, if not more, if the cost would be close to what Varane cost last summer (under £50M in transfer fees and £200-250K weekly) then I am 100% supportive of it.
The contentious point is the huge outlay, let's say for argument sake that the outlay is 400K weekly on a 5y contract, for fee of £70M++.
At that amount of money mentioned above, If a team is already doing well, with a mix of great players (young and experienced), then adding someone like Casemiro, even if it is on a huge salary and huge fee, it would be understandable/acceptable, as it will propel the team higher and offer a greater chance of success, an example of this would be Alaba to Madrid, although it was a free transfer, RM paid him a huge salary and it was worth it for them.
But, for a team like United, that has a lot of areas that require immediate improvements, and
these improvements has to be of certain age in order to allow the club some room for long term planning (e.g. Malacia, Martinez, maybe De Jong?), spending such money (400K weekly on a 5y contract, for fee of £70M++) is a waste and such money can be diverted to getting more players who are younger than 30 years.
What I said above is the principle of the matter, and coming back to reality, the bigger problem for me is the lack of planning once Ten Hag accepted to be the Head Coach/Manager in late April this year, 3 signings aren't enough and more players were/are needed to elevate the current level of the squad and it is late in window so it is panic time for the club, but at least getting Casemiro, even on a huge fee + salary, is a far better option than getting the likes of Rabiot, so as a panic buy, Casemiro is the best option to "Panic Buy".