What was his birth weight? 100g per week / 3.5oz per week isn't as fast as suggested but its not drastically slow. How old is he?
Did she suggest having the tongue tie divided while he's little and that can help him transfer the milk better? Did she suggest breast compressions to help him get a bit more milk - if transfer is an issue, that might work better than pumping and bottle feeding.
Have you done a weighed feeding so you *know* what he is actually transferring?
f he's not emptying the breast effectively, yes, I would try pumping just to avoid mastitis and maybe have a bit on hand for growth spurts, etc or build a stash if you so desire but really, if he's struggling to transfer milk, you want what he does take to be as nutrient dense as possible, so stimulating an oversupply is probably not a great idea.
What was this lady's qualification? I'm not qualified in this area, however I would have thought it would be best to address the physical issues of tongue tie and swallow coordination - yk, address the cause and not just treat the symptom so to speak.