In my Sauromatae campaign the Seleucid have grown huge and every turn I get a stack or half a stack besieging some of my border provinces, for a few years I've gotten many heroic victories and destroyed their armies but they keep coming and growing bigger as they will son overwhelm the Ptolies and eliminate Baktria and Parhia.
This is how it looks:

In my previous campaigns (Casse and Romani) they always started strong but as Hayasdan, Parthia, Baktria and the Ptolemies allied they were devoured piece by piece by their combined effort, but since I played the Sarmatians Hayasdan and Parthia attacked me and I had to respond so the Seleucids grew this big...
I'm getting kind of tired of their phalanxes and feel like I'm in a stalemate because my economy is barely in the black and keeping my empire together because it's so big and with few cities that are far apart is really hard, I use a mobile capital but it's annoying.
Maybe there should be some more law bonuses from the government buildings because keeping a garrison of horse archers is costly.
Anyway anyone ever faced something similar, what can I do?