I was told the same thing after I had Pie.

With DS2 I had used them for about 8 weeks and then moved to the breast, no problems, no supply issues, easy peasy.

When I had Pie & was struggling with her attachement - just that she wasn't really motivated - I asked for a nipple shield (still in hossy) as I had used them successfully with DS2. I was told by the hospital LC that they didn't use them anymore, they would dry up my milk & she would get in trouble for giving them to me. She said she had more success getting babies back to the breast form a bottle, than from a shield.
On the basis of that advice I went home bottle feeding, and never got back to the breast.

So... my 2c... I know you can't discount all the studies & knowledge that is out, there , and who knows - we may be the exception that proves the rule - but I really , really thinnk if everything is working for you then don't mess with it! Be mindful of it, if your supply takes a big dip be aware that may be a reason - but what you are doing now is working. If it ain't broke.....