The bag is not the problem
As with tea, the bag is inert. What is inside it is a commercial decision, and in herbal blends that decision is usually to use small-particle material because it extracts fast enough for a three-minute cup.
Why particle size matters more here
Many botanicals are structurally fragile — flower heads especially — and milling them destroys the thing you would use to judge the material. Whole chamomile flowers are recognisable and their condition is visible; chamomile dust could be anything, dried at any temperature, in any year. You lose the ability to assess as well as some of the flavour.
The ingredient order is the real signal
Herbal blends are where ingredient lists earn their keep. A great many fruit infusions are mostly dried apple and hibiscus with the named fruit well down the list, because apple is cheap and supplies body. This is entirely legal and entirely uninformative unless you read the order.
Where bags genuinely win
Portability, and anything you will drink at work. An empty fill-your-own filter bag is the honest middle: your material, their convenience, and it costs almost nothing.
What to buy
Whole material for anything where appearance carries information — flowers above all. Cut material is fine for roots and grains, which you cannot assess by eye anyway. And buy in quantities you will finish, because aromatic botanicals fade faster than most people expect.