Immolation needs to have a "boosting condition"
When you look at similar immolation effects in HotS, they each start with low base damage, but get bonuses if certain conditions are met. For instance, Johanna's version has low base damage, but for each enemy Hero she hits with her Condemn ability, the damage is increased by 40% for a short time. Good to give it power in team fights, without making it broken in pushing.
Sunfire Cape, IMO, needs to be similar. Lower the base damage, but do something like having it increase for every nearby enemy Champion (small radius). This way, it becomes threatening in clusterfuck fights, but won't make a split-pusher OP.
Could something like this work?
