Dang, #2 as minimum seems like a really high standard. I've never been a terribly strong person though. No disagreement on strong grip's general defensive benefits. Sometimes I feel like I ought to get back to the Captains, but my arms and hands feel like they have enough going on already. When I overdid it before, I was working the 1.5 and changed from doing it twice a week to three times a week. Didn't feel like it would be too much, then ouch, it was suddenly too much apparently.
That position doesn't seem right to me. I started shooting with the crossed thumbs grip and experienced improvement as soon as I went to thumbs forward. I'm sure I had a lot less grip strength at the time. The benefit of the thumbs forward grip is that it gets maximum skin to gun contact, which leads to controlling the recoil through friction, and consistent and predictable movement of the gun in recoil since the gun's grip is fully surrounded with hands. The foundation of the grip is not dependent on a lot of strength, and I think more grip strength is going to help any grip, whether it is thumbs forward or crossed thumbs.