Your question conflates two questions into one:
- Did the IIgs sell more than the Mac in 1986?
- If so, why did the IIgs sell more than the Mac?
Others have given valid reasons for (2), but there is evidence that the answer to (1) is "No".
For instance this source says the Mac sold a million units by 1987, which is about what the IIgs sold over its whole lifetime - according to a former manager of the Apple II division quoted by Brutal Deluxe in their project to collect IIgs serial numbers and estimate sales data.
The Mac number roughly matches Jeremy Reimer's sales data which he used to write this article, and which I used when answering "Over its lifetime, how many Apple II computers were sold?"
Scaling Brutal Deluxe's estimated sales data by the 1 million IIgs limit gives about 122,000 units in 1986-1987 (peaking at 305,000 in 1988) vs the Mac's 380,000 in 1986 alone (900,000 in 1988).
It was the Apple //e that funded development of the Mac - until around 1988 when Macs finally started to sell more than the whole Apple II line. The full data for Apple II's and Macs from my other answer is in this Google Docs Sheet, with various notes about assumptions etc.