You are technically not incorrect when it comes to the short-term buff + summon trick. At one point, yes that was possible. I am pretty sure it was hot fixed because I tested it on a training dummy last week with Garuda summoned normally, and Garuda summoned after drinking a Mega-potion of Intelligence, and there was no difference in damage.

When it comes to the scaling from gear itself, I have not tested that yet but you can try testing it on a training dummy with your gear equipped and then taking it off.