I was expecting this, but at least I'm not posting the same exact thing every week or so.
I just put it in some relevance to the discussion, you can go ahead and even quote me if you want on that.
Plus I would say that I am not the only one of that opinion and it's a serious matter for the viability of the entire British Army, not just one commander or unit.
You may be presenting more arguments, but I think testing what you're suggesting is currently out of scope, considering it's a commander revamp patch and the only two (?) changes outside the revamped commanders were rather small and critical. It's mostly a community patch, with a balance team that doesn't have full authority over what they can and can't do.
---
That said - IMO
I think such an artillery pit would simply be ignored by British players and UKF would just become the fourth faction with a mobile mortar. A static emplacement that gives 15% more range and only gives extra protection against small arms doesn't really seem worth the 100mp investment, especially when only getting one mortar. The strong, static mortar pit is part of what makes UKF unique, so if you want to maintain that uniqueness while giving both options, you'd have to atleast make the mobile option weaker than those of other factions, while making the static option stronger. This seems pretty hard to do right to me.
If you simply want the mortar pit to be more flexible, I think a dismantle option would be a step in the right direction. That way UKF has more control over their popcap and can react better to shifting engagements. The resources you get back could be made to scale with vet, starting at 33% (at 100% hp) up to 66% for example. This way, the Brit player will try to get the most out of it, while giving the axis player more incentive to kill it. Ofcourse, the dismantle option would take some time and can't be selected while being braced or in combat. What do you think about such a change?