Axis Invasion would be an amazing game mode if they changed this.
If they would make the invader invulnerable to mines I think the invader game mode would be waaaay more enjoyable.
I get that the campaign player needs to have the inherent advantage. Overcoming this disadvantage is what makes winning as the invader feel so rewarding.
There is however no reason for the invader to be vulnerable to mines as well. Mines make an invasion go from terribly balanced challenge, to completely unfair and uninteractive gameplay. A mined map promotes the invader to camp and not engage with the map at all. Also a mine kill feels unrewarding as there is no interaction between the 2 parties.
The focus wallhack already discourages the invader to close the gap. Adding mines to the equation makes it impossible to get close to the Karl/Harry. In order to win against someone with wallhacks, you need to close the gap fast before they notice you are there. But when playing around mines, you can't run around. There is also the added effect of a camping Karl/Harry seeing you disarm a mine (with focus) and then being able to get an easy kill on you.