thats actually a fair question, no technically if you declare you're going to attack with both weapons, it doesn't matter if you use the bonus or the standard first. Because you already declared both. Not sure how you'd implement that in BG3 though, other than after using bonus action attack, disabling everything except the attack option...
i liked the flexibility of taking offhand attacks first. i had a dagger that gave bless on hit that i was using in my offhand so i was making offhand attacks first so that my main attack would be blessed.
