Efficiency of having 2 heat pumps in my house
Without the performance curves, it's impossible to say, but in general, equipment is more efficient when it's not operating near either the maximum or minimum load, so yes, it's possible that two units, each operating at 40-70% of their rated capacity, could be more efficient than a single unit operating at >90% of its capacity.

This link is actually about computer power supplies, but it does illustrate how many performance curves look. Realistically, this should serve to illustrate proper sizing so normal operation is near peak efficiency with peak performance matching maximum anticipated load.