too much talk and pseudo experience.
Fish can adjust, even in their natural habitat, there is wide range of condition due to dry/wet season, river/landlock water body...,
heavy tannin water or not, make sure you keep the water clean and avoid fluctuation.
From other angelfish keepers personal tanks, I know:
altum angelfish are a lot more delicate, but slowly adjust, they survive well in a planted tank with PH as high as 8.5. and TDS as high as 500.
wild angelfish have no problem in these water condition, they are hardier than altum anyway. the key is to slowly adjust, avoid sudden change.
I will try altum when the season come, my tank is ready, the pH can not go higher than 5 no matter how much water I change, typical old tank syndrome.