ideas to boost slavers:
maybe slavers raiders (from CS only) could get slaves by pillaging improvements? (lower odds)
maybe slaves could be added to city as "slave specialists", or "better", be sent to work on improvements :
slave can take action on top of basic worker actions :
only one per improvement: "work mine" on mine : +2p/turn to nearest city, "work farm" on farm : +2f to nearest city... etc,
can be "sold to citizenry " in city : slave specialist: -1f+1g+1p+1c (total +2yield...),
can "amuse the citizenry" : (fake building with +1 happiness)
...Etc
can turn feral (weak barbarian warrior) or disband if no nearby military unit.
tradition's science policies seems strong... compared to other policies and traits
idea for engineers early/late actions:
-build bridge (over 1 tile of water/ over river: increase commerce/ movement...?)
-build podler (for civs that don't have that possibility/tech)
-build improvements in place of worker but much quicker
-build some buildings in the city in x turns (depending on mod, minimum 3turns) (so the city can build settlers/units, and the engineer build the walls ...etc)
-build improvement without adequat techs but at slower pace than worker ? can only be done once per Eng per improvement? (eg: deep mine without the tech or plantation ...Etc)
-Magic: I agree that it would be nice to have some spells targetted toward replacing normal acitivities by magic, or sustaining civilian magic:
I don't think it'll enable magic line to be more powerfull than a production focused or culture focused:
example : illusionnists can cast a spell (can be automated): Illusion show: +mod/2 c, +mod/2g or increase happiness
Conjuration enable "magic forge" : +2p-2mana, and conjurer can "work the magic forge" +mod/2p, +mod/2c
summoners can "summon workforce : +mod/2 p" (in exchange mod mana)
...etc
you could have "magical preserves" that are improved granaries but cost mana/turn, and are insta-built by mages using mana or that give more health.
a diviner could "help the local autorities" and decrease discontents, decrease maintenance,
a sorcerer could "sell crux and maledictions" : +mod/2 g, decrease discontents, increases maintenance
a type of witch could heal the livestock : fake building: +1f+1p per local cattle/horses/elephant, -3mana
If it is done correctly it will not enable an arcane civ to overwhelm a non-magic civ on their specific area... but it will bring diversity to the arcane line (techs AND Units) by enabling applications that are not dedicated to war (damage, unit support or ennemy vision...etc)