thats right it is a way of stimulating the immune system to action. The problem is that some mistakenly believe that a synthetic adjuvent is required for a vaccine and it is not.
the adjuvent increases the gain so that you can use a faint signal- that means less mRNA has to go into a vaccine that means this expensive little molecule can be used for many more doses instead of one enormous dose of high concentration, as mentioned before if we needed adjuvents for immunity of any sort we would not be here.
the substances you are mentioning are features of live pathogens and are being mimicked by adjuvents.