your right
imagine there were 4 CEX
EU , UK ,NGN, KES
the most efficient method of swaps is
the image above is not LN. its just back office reserve swaps so fees are negligible if anything no matter the value. but emphasis this is not LN
however in LN at the most efficient swap, (i limited it to avoid hours of channel making doodles)
but this runs into issues
liquidity availabe if channels have already processed $x amount the night before
and also
not all channels will have equal balance. even if not used before
and also
not all channels have equal fee's
it requires several hops along a route which even in a 4 hop network is a 4x of fee per channel
ill leave you all to play out scenarios on that
(by the way most LN nodes dont have $2k channel balance)
oh last thing
many LIGHTNING devs are playing with a system of using $stable coins as the backed unit of mCENTS on LN thus no need for a fiat-btc-msat double conversion on the entry nor a msat-btc-fiat double conversion on the exit
they instead deposit fiat and use stable coin in LN