i'm fully with you on (legal) trade.
i haven't tested smuggling myself as extensively, and more so not recently, but
a) profit wasn't effective in smuggling in 2017, while it was in trading (see the outdated 2017 thread
https://forums.frontier.co.uk/threads/bgs-trading-for-influence.357715/, smuggling boom vs. none - it did not make sense to me back then, but i even didn't consider smuggling dealing with galactic average).
and
b)
@PaulieWotsit shared his findings of galactic average doing for smuggling what profit does for trade in some thread here ... i'll try to hunt it down, but when reading his findings it made sense to me, because stolen goods have no purchase price.
formalising it:
trade profit positive: influence gain, economy up.
trade profit negative: influence loss, economy up (!).
smuggling profit positive or negative: influence loss, economy down.