>Were they wrong? People who rely too much on a calculator don't develop strong math muscles that can be used in more advanced math.
Yes. People who rely too much on a calculator weren't going to be doing advanced math anyway.
Yes, they were wrong. Many young kids who are bad at mental calculations are later competent at higher mathematics and able to use it. I don't understand what patterns and tricks you're referring to, but if they are important for problems outside of mental calculations, then you can also learn about them by solving these problems directly.
Were they wrong? People who rely too much on a calculator don't develop strong math muscles that can be used in more advanced math. Identifying patterns in numbers and seeing when certain tricks can be used to solve a problem (verses when they just make a problem worse) is a skill that ends up being beyond their ability to develop.