I don't think high P kills mycs as much as renders them dormant/unnecessary. Obviously in natural soil outdoors this would mean it wouldn't be as abundant and able to sporulate so over time would be depleted (hence the problems in agriculture today with sterile fields & increasing fertiliser requirements), but when added into compost in pots it should just allow you to feed a bit less while gaining some extra drought resistant/tolerance, and possibly an enhanced mineral leaf & fruit profile.
Some studies almost conversely suggest that in a very nutrient rich environment some species of mycorrhizae don't go dormant at all, and instead become a net drain, losing their mutualistic give and take with the plant and costing you extra nutes in the long run :thievingmushroom:
We need some side-by-sides with organic mixes v a normal mp potting mixes both with innoculants to tell really (ideally a myco only innoculant to ensure that it and not the rest of the 'beneficial' fungi and bacteria, seaweed, humates etc in the pot are responsible) the organic mix would hopefully be more efficient with fert use, or at least the myc plants should maintain the same level of health and growth with less fert requirements...
Similarly it would also be good to test myco innoculants with a very light organic mix, innoculated vs a control..
The fact mycorrhizas can increase leaf and fruit mineral content could actually be a bad thing, thinking about it, some plants have shown a greater ability to uptake/a higher tolerance of arsenic and other poisonous substances..