About 20 years ago (or more) I bought a friend of mine a TOS cast t-shirt because he loved TNG. Loving my gift
he took it away on a holiday to climb the Himalayas where he would be camping and staying in huts without running water and electricity.
He came back and he told me that he was amazed how many people recognised the people on the shirt. In places without TV or movie theatres where they didn't speak English, people would come up to him and say 'Kirk', 'Spock'.
So you claim they're not icons but a lot of people around the world recognise them.
Ever since My So-Called Life came on in the 90s, I have been told by almost every stranger I meet that I looked like Claire Danes (I do have an uncanny resemblance to her- this poster picture could easily be me
). When lived in Japan 10 years ago, even Japanese people would tell me that I looked like her, and I'm pretty sure she wasn't an iconic character in anything as popular as Star Trek. The actors are not the icons...the characters are. I bet that if you showed those same people a poster from the new Star Trek, they would still say that those characters were Kirk and Spock.
If they were in the yellow and blue shirts, yeah. But if you show them a picture of these guys doing the DRESS GREY thing, a decent guess would be 'is that STARSHIP TROOPERS?'