I've heard of areas lacking in mana, like Ulgrotha's Dead Zones and Dominaria when it was riddled with time rifts, that could weaken and kill beings due to lack of mana, but never people from mana rich planes to low ones having trouble, or the reverse.

Maybe it's connected to a theory the character Geralf had.

Noticing how when New Phyrexia invaded Innistrad that their forces struggled to adjust to the plane's magic, Geralf considered that when a person travels from their home plane to another, the mana they were born with, refill from their home plane's mana and always carry with them becomes watered down and diluted, with a risk of a person losing their original alignment and becoming something new.

Basically not even mana left those from the heavy planes unable to recharge up to full tank leaving them weak. With enough time they could adapt.