They have written endlessly about the Grail. Again... All these rules have been around since the time when only one template was played - 2SM4d(3)(on the L+U map). Now there are about forty templates played, and the rules are changing more slowly, and although features are being created for different templates, the former basic formulations are changing with some reluctance. It is simply necessary to exclude ambiguous (non-universal) interpretations from the basic set of rules and place them in template-specific features (perhaps, one day each template will be the same module as we have now "HW rulez" - as, in fact, a prototype).
Regarding the Grail, it was long overdue to move everything from a forbidden dead end. Prohibitions are always a limitation. There have been countless discussions, there was a discussion about which week to start digging, and there was a discussion about how much they were afraid of the Grail for the Conflux and the unfortunate "imba" Tower. I have always dug for the Grail. This can be a kind of joker up your sleeve (especially important for balance and similar things) and a fun puzzle. The computer digs for the Grail from day one. Why not allow the player to do the same. Digging for the Grail is a very troublesome and expensive undertaking. And it is not done out of a good life, often precisely in critical situations. You can simply shift the timing of the Grail installation for each template and define additional conditions (and focus on this in the mod).
Regarding the balance in this context, you can not worry about it at all as long as there is a sphere of suppression and a cloak of renunciation; the installed Grail will be more sensitive for small L+U templates and less so. The balance can only be in general, and in particular, only strong shifts in one direction or another simply need to be correlated, but not prohibited.
It turns out that the value of this patch for a player who knows the rules is practically zero.