This is more a general question of how you handle them.
Because in my mind, they won't always have a vehicle.
Making their vehicle use infrequent makes the specialty not worth it, while if you want them used often, you have to tailor your campaign around the fact they have a Leman Russ with them.
It's just that, in my mind, V-Scale and P-Scale can be very separate.
So how do you plan around this? What do you do as a GM?
If someone in my group wanted to be an Operator, I think I would simply just assume a vehicle for the majority of the campaign; I don't see it as that big of a downside, and it makes a lot of sense for a OW regiment to be mechanized. Also keep in mind if you're worried about vehicle balance, you can always just issue them a Chimera instead of a Lemen Russ, or something similar.
If you dont want to deal with, just calmly discuss it with said player and see if they want to play something else. Perhaps appease them later with a vehicle segment in a campaign.
Regardless, the beauty of a traditional RPG is the freedom you have as both PCs and GMs. My personal goal as a GM is to create a world and story that my players will enjoy, so if a player wants to be an Operate, I will adjust the world to make that happen.
I also personally love they included vehicles off the bat, as opposed to DW, for instance, that added them later. It definitely potentially adds a lot of variety to gameplay scenarios (and my players are still clamoring for a Titan in one of these campaigns, someday…)