Why shouldnt you pay. If its personal use why should the employer subsidise that.
My point is if you dont use a personal device on the corporate network paid for by your employer and instead use the personal device on the cellular network you pay for, then you will be "secure from MITMs".
I'm not saying the employer should subsidize it. Some employers might. If your employer provides that perk, it might make sense to use it. Similar to how if a restaurant provides free wifi it might make sense to use it.
I think the real way to be secure from MITMs is to use a device that you control the root CAs of. If you control the root CAs, you'll be safe no matter what network you're on. If you don't control the root CAs, you'll be vulnerable no matter what network you're on (but some networks will carry a higher likelihood of an attack).
My point is if you dont use a personal device on the corporate network paid for by your employer and instead use the personal device on the cellular network you pay for, then you will be "secure from MITMs".
More than one way to be "secure from MITMs".