Well then John .... I ended up having to go through the video twice as I got a different total to you!!
I counted thirteen Motown recordings, plus two non-Motown recordings of Motown songs and "We Are The World" (which had some Motown artists in the chorus line).
My count of 13 comprises of 5 Lionel Richie solo efforts, plus his collaboration with Diana Ross, plus 2 Diana Ross solo efforts and two Stevie Wonder solo efforts plus one each from DeBarge, Rockwell and Rick James. Of the two Non-Motown covers of Motown songs one I was very familiar with, the other was new to me!!
As a general rule I prefer mainstream '80s Pop/Rock music to the '70s equivalent but it could be very formulaic and this shows on this list ... I was surprised to see how well Sade was represented and both Michael Jackson and Whitney Houston seem to be as popular as ever. I wouldn't have guessed the number 1 but it didn't really come as a big surprise and I never realised that Metallica were quite that big.
The poster has added a new disclaimer stating that he has excluded a lot of recordings on the basis that they "were not well known in the US (because being honest 82% of this channel's audience is from North America and they probably don't want to sit through 50-100 songs they have never heard)" ... doesn't this negate the whole purpose of this exercise?
Anyway ... I'm looking forward to hearing y'all identifying both of the two non-Motown covers of Motown songs.

Roger