Energy expenditure at threshold pace is really similar between the two and there's a lot of carry over between running and cycling. That's why triathletes run fast despite running, by runner standards, not very much. Similarly, whenever I rode a bike together with someone who can run a sub 18 minute 5k, well, they weren't slow, and some were blazing fast. For me it's a bit skewed in favour of cycling because I do much, much more of it (my running amounts to one or two one hour runs at a talking pace per week) and my morphology is the antithesis of what makes an efficient runner, and maybe I don't dig as deep when running because of simply not being used to it - which seems to be the case looking at heart rate.
Running my 5km flat out pace is 4:13 for around 21 minutes time, over a slightly hilly course, which equates to about 910-950 kcal/hr depending which source we take, at a HR of about 165. Cycling, the best power I can do for the equal amount of time (so 21 minutes) is 290W, which equates to about 1040-1050 kcal/hr, with a HR of 169. Over longer distances, I can run a half-marathon over a hilly course in 1:43, which amounts to about 850 kcal/hr. Cycling I've done 254W for that duration, which is 910 kcal/hr. This is all not counting BMR.
That's really not that much of a difference and understandable given the massive difference in the amount of cycling and running I do (and again, short but muscled legs is not what you'd consider a runner's physique). On a cycling ramp test runners might do more poorly than you'd expect, but that's partially an artifact of how testing is done - it increases the force required, while on the road, we have gears and for most climbs they're adequate.