If you check this link from Gngram you will see that your phrases paramount advantage and pivotal advantage are not very frequent. At least not as frequent as expressions like
a pivotal role or of paramount importance
(You can find more examples at WordHippo)
With advantage, you could choose one of the adjectives suggested by Gngram, among which I think decisive or essential seem to be the closest to what you need.
However, just because Gngram finds rare instances of an expression does not mean you cannot use it. I actually found quite a few examples on Google, among which:
But ultimately, the most pivotal advantage came in the form of a
clearer, more utility-focused view of customers that helps accelerate
sales cycles and improve service. (from digitalistmag.com).
I also found quite a few results with the most paramount advantage:
The most paramount advantage to the use of transporters like PEPT1 and SMVT is the potential for increased oral absorption. (from an article on the ncbi.nlm.nih.gov site)