Is there any other reasonable way to get from Pattaya to SS and vice versa than by taking minivans to/from Victory Monument?

I prefer a normal bus with a.c., normal travel times and bus stop in the town centre of SS.

There are multiple sites stating that regular buses to SS go from the southern Bus terminal on Borommaratchachonnani rd.

(served by the http://home.transport.co.th/index.php/th/)

I haven't checked about buses from Pattaya to the southern bus terminal?

Would surprise me if there aren't.

While I haven't used them myself, I once did some research for a friend who did. In general, departing the North Bus Terminal on North Pattaya Road from approximately 8 a.m. to approx. 12 noon, then a long gap with departures beginning again about 5 pm. This schedule is designed to avoid Bangkok rush hour traffic. Running time to Sai Tai Mai (Bangkok Southern Bus Terminal) approx. 2.5 hrs.

Maybe check one day before your intended trip; my research on this topic is about 7 yrs. old.