It can be less intrusive, but it depends how the person in charge of mobility set things up and the MDM tool capabilities.
On Android you can define a device as corporate owned, which mean the employer have full control over the device, or it can be user owned and instead of taking control of the entire device, it makes a sandbox in which the corporate data resides, and the mobility admin can only touch what is inside that sandbox. If the phone is lost or the employee leave the business, you can remotely wipe the sandbox while leaving the user data untouched.
IMO this is a better approach, but it depends on how the system is set up.
Personally, that's still an unacceptable approach. There is no way I'm going to allow any employer to have any degree of access to my phone. If my employer needs me to use a phone for work purposes, my employer needs to provide a work phone to me.
And that's entirely your right not to use your personal device for work, and I agree with your position, while some others might be more lenient and will accept to have it on their personal device for the convenience of carrying and charging only one device.
It's nice having some flexibility for the different mindsets, but as long as the tools are provided by the employer when they're mandatory I don't see a problem.
On Android you can define a device as corporate owned, which mean the employer have full control over the device, or it can be user owned and instead of taking control of the entire device, it makes a sandbox in which the corporate data resides, and the mobility admin can only touch what is inside that sandbox. If the phone is lost or the employee leave the business, you can remotely wipe the sandbox while leaving the user data untouched.
IMO this is a better approach, but it depends on how the system is set up.