I can expand on that idea as well.
Increase the cost of the Bofors from 280-mp/30-fuel/10-pop to 320/60/12 and decrease the range of its suppressive barrage ability from 60 to 50. The Bofors will still be extremely strong at locking down a point against infantry and vehicles but the cost increase will force the UKF player to seriously consider what route he wants to go. If he buys the Bofors then he will seriously slow down his Cromwell. If this is seen as too drastic of a nerf (which I don't believe it is) then a potential alternative is to up the cost of the initial side tech and lower the cost increase of the Bofors. The change in its suppressive barrage range is just to prevent it from countering indirect fire (something it wasn't meant to do).
In addition to that change:
Increase the population cost of the mortar pit from 8 to 12.
Decrease the population cost of the 17-pounder from 20 to 14.
The result of all of that together would still allow for sim cities to be a completely viable strategy (considering how powerful all of those emplacements are) but not nearly as cheap and easy to pull off. If the UKF player decides to go with the sim city route then it will heavily punish his mid-game (slower Cromwells) and even his extreme late game to an extent (due to population increases). In total, I think it would allow for a much less frustrating experience for Axis players and a greater strategic diversity from UKF players.
320/60/12 is still pretty low compared to a double ost mortar or tanks. It should be more increased to at least 420/40/12. Why? Because it can kill medium tanks, insta kill infantry, big range and ultra resistant. It requires a lot of micro to kill it. Because lets face it, if you start tickling it, you will see mortars or blobs incoming 5 secs later. Emplacements are rarely left undefended..., add to that their mortar range and in 2v2 you lock the 2/3rd of the map, and send your troops attack the last third.
I don't have such an issue about the actual power of bofor, more their resistance.
When braced, which is free, they take almost no damage from everything. Even a tank is not that hard to kill. This is particularly annoying when using sector artillery or when you have spared enough ressource for one rocketenwerfer. You will use your resources for nothing if he braces it at the right time. Then wait 90sec to reload and do it again
Emplacements should either cost way more or and be more vulnerable. Brace should reduce the damage to only 50%.
MHT might be a good counter, but should I choose my commander because of only one or two units he has on the field ?
Yet, don't forget the counter barrage ability, able to destroy any indirect fire unit on the field on small maps, meaning 1v1 2v2. This makes your mortar free target practice for the brit.