Their promotion tree need a little rework, needing two promotions to actually be good at exploring hurt them a lot, and most other promotions offer little value, here is my idea for a reworked promotion tree:
merge Ranger and Alpine, replacement for the missing promotion, no movement penalty on river crossing, can scale cliff walls.
Sentry get +10 healing in neutral territory
Spyglass get reveal stealth units with sight range
Guerrilla get ignore zone of control
Ambush merged with Camouflage
Camouflage replacement give +1 range & +1 movement (or additional attack if movement allow)

also, maybe something similar to this
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2282934791