I assuming he means insanely more efficient than they used to be, not more efficient than ground-source (awkward wording though). I suppose they can also be described as more efficient in installation time, cost and equipment than ground source, but clearly not in operating efficiency.

Yes air source are really good value in cost effectiveness terms, especially when a house has an existing central heating system they can connect to. But their COP - whilst dramatically improving in the last 10-20 years - is still behind ground source, particularly in the north during winter