> while their others series are solid but with a more niche player base

Might have been so in the past, but Paradox games are relatively mainstream, although they seem a bit niche.

Hearts of Iron IV is the 32th most played game at Steam right now (https://steamdb.info/charts/), while Cities: Skylines is on spot 56. Might have something to do with recent news or released addons, but still, other Paradox games are wildly popular and Paradox would surely do just fine even without Cities: Skylines.

More interesting stats comparing Hearts of Iron with Cities: Skylines

> Cities: Skylines - 18,280 players right now | 24,541 24-hour peak | 60,386 all-time peak 8 years ago

> Hearts of Iron IV - 32,652 players right now | 44,193 24-hour peak | 70,997 all-time peak 5 months ago