It's amazing how far the balance team have gone to avoid actually touching the Churchill's performance, same goes for Volksgrenadiere.
Because making changes to "secondary" unit stats (like cooldowns, build time, abilities etc.) has proven to be a very good tool to balance units by adjusting their availability or timing, without having to nerf their performance. One major advantage with this is that it allows for units to remain strong to keep them attractive to use, but helps prevent them from being deployed in quick succession and/or in overwhelming numbers.
In the last 2 patches units like Pathfinders, Assault Grenadiers, Valentine and Jaeger Light Infantry all triggered a vast amount of complaints after their initial timings or performance changes about overperformance, and ultimately they have been fixed without touching their performance at all just by limiting their availability (I have barely ever seen any complaints about those units since the follow-up patches). These small changes are usually way more effective than people initially think.
As for the Churchill specifically, I personally do not believe a single Churchill is overperforming (except that grenade ability they had at vet 0), and that the unit is only really problematic when deployed in overwhelming numbers (~3 at once). So from my point of view, there is no reason to overly punish players using 1 or max 2 Churchills in a diverse build by nerfing the unit's primary performance.
So for now, availability will be more limited to see if that alone works, and if ultimately it doesn't work, performance can always still be nerfed later. But the first option is preferred.