I don't think this weakens my argument at all. It is fact from 1E to 5E, the official maps of Faerun are off by quite a bit. Looking for an in-game explanation isn't unreasonable as the fact that the map distances are off is... well... fact. But don't take my word for it... Elminster's Guide to the Forgotten Realms says the following about maps:

Maps in the Realms are expensive works, being rare, easily damaged or destroyed, and more often inaccurate than not. Large, detailed, good maps are usually owned by rulers, from mayors of cities who have sewer and street maps, up to kings who own large and varied collections of old and fanciful maps from everywhere.

....

Nautical charts tend to be cruder, more inaccurate, and even more precious than maps.

Is Elturel 200 miles as the crow flies from Baldur's Gate, or is it 215 miles from Baldur's Gate? Apparently, even cartographers of the Realms cannot agree.