I don't think that's 100% accurate. I had a look at the report that this article is based on when it was first published and (I think*) I recall it was looking strictly at propolis products rather than all carp care treatments.
I have mentioned several times on here, way before this stuff was published, that I question the use of propolis in angling. The use of propolis originates in koi keeping. It creates a barrier on the wound to lock out any nasties rather than act as an antibacterial/antifungal solution (although dodgy marketing from the tackle firms would have you believe otherwise). This barrier effect is fine when a koi is living in a posh pond with clean, filtered water with controlled salinity. Not so fine for a carp lake - my opinion is that you risk locking nasties IN to any wound.
There are other (non-propolis) carp care treatments options available that are genuine antibacterial/antifungal treatments. How effective they are is open to debate but one thing is for sure - they cannot do any harm to the fish. Even if it washes off straight away you can be safe in the knowledge that the hook-hold or wound was completely free of anything that could result in infection when you send mr carp home.
My overall opinion is: we don't really need to use treatments, but if the right treatment is used, it cannot be a bad thing.
Propolis is actually the "mortar" that bees use to build there hives! I think it's a mix of beeswax, bees spit, and plant resin. Clever little [censored]s aint they!