I'd have to agree about him being unplugged. I don't think he's ever been audible on guitar, perhaps in the late 70's and early 80's when he was plugged in, but certainly not in the last 30(ish) years, where usually his guitar isn't even plugged in
honestly, I think it's just part of his shtick, and like Brian and Bruce, doesn't have the frontman gene like Mike, and needs an instrument to not look/feel awkward. I've been singing onstage for years, and I'd feel naked without a guitar or piano, even if I wasn't playing something incredibly complicated or important- or even playing at all.
Those 2016 clips are pretty cool. It's fun to see Mike and Dean joking around. I wish Mike would still play Surf City, just to hear Bruce's falsetto in the chorus alone! Dean's vocals, even when he's not singing lead, add a layer of authenticity. Even though he's not the best singer in the world, his voice is so unique, and instantly recognizable. His falsetto can cut through the blend perfectly, and in his mid-range can fit right into the Beach Boy blend.
When I saw Dean in concert he sang everything from bass parts, to Al/Carl midrange harmonies, to lead falsetto. Falsetto probably 70% of the time, be it lead or in the harmonies. Compared to Brian and Al who need Foskett or Matt Jardine, and Bruce who only shows off his falsetto in the outro of the final song, I was astonished to hear Dean hit such high notes, with seemingly no effort at all. I'm talking "New Girl In School", "Sidewalk Surfin", top part of "Sloop John B", top line of the "Goood Good Goood Vibrations"... this was a man, in 2019, singing in his same falsetto voice that made him famous in 1959. It blew me away.
When I met the band after the show (Before Dean came) I was talking about how well Dean's voice has help up. Phillip Bardowell made a point to make sure I told that to Dean. Well I did, and sure enough, he lit up. He told me that he has to stay conscious of how much he sings, and take breaks, and warm up, etc... He was obviously being truthful, but to some degree, I also believe humble. He made it look too easy.
His voice is an often overlooked, crucial, ingredient in the California Sound. And before I get the people saying "Jan & Dean couldn't sing", well obviously they didn't have the perfect pitch of a Carl Wilson, but their voices were unique, and cut through a mix very well.