As well as other mid-1960s pop bands and acts like The Mamas and the Papas, The Dave Clark Five, Herman's Hermits, The Buckinghams, The Association, The Lovin' Spoonful, The Byrds, and Donovan? Was it due to the arrival of Jimi Hendrix and psychedelic rock/acid rock, which signaled the start of the hard rock era and the implicit need for guitar virtuosity?

Roger McGuinn of The Byrds had a LOT of "guitar virtuosity." I can't believe you'd place them in a group you believe has become "irrelevant." Highly influential.

As well as other mid-1960s pop bands and acts like The Mamas and the Papas, The Dave Clark Five, Herman's Hermits, The Buckinghams, The Association, The Lovin' Spoonful, The Byrds, and Donovan? Was it due to the arrival of Jimi Hendrix and psychedelic rock/acid rock, which signaled the start of the hard rock era and the implicit need for guitar virtuosity?

How in the world did you come up with this question, Jimmy Hendrix was not a Top 40 act the others were. Hendrix had only one top 40 song that peaked at number 20 (All Along The Watchtower). Acts come and go all the time, they string some hits together and then they go cold. In the late 60's early 70's The Guess Who had 5 top 10's including a number 1 went cold for about 4 years had one more top 10 before disbanding, Blood, Sweat & Tears had 4 top 10 hits over about a year and a half including three songs that peaked at number 2 and then they went cold. The point, it happened all the time you can look at any point of the 50's, 60's, 70's and 80's and find the same thing, it's the nature of the business.

How in the world did you come up with this question, Jimmy Hendrix was not a Top 40 act the others were. Hendrix had only one top 40 song that peaked at number 20 (All Along The Watchtower). Acts come and go all the time, they string some hits together and then they go cold. In the late 60's early 70's The Guess Who had 5 top 10's including a number 1 went cold for about 4 years had one more top 10 before disbanding, Blood, Sweat & Tears had 4 top 10 hits over about a year and a half including three songs that peaked at number 2 and then they went cold. The point, it happened all the time you can look at any point of the 50's, 60's, 70's and 80's and find the same thing, it's the nature of the business.

I never said or insinuated that Jimi Hendrix (https://missionengineering.com/10-reasons-jimi-hendrix-is-the-goat/) was a Top 40 act unlike those other artists (https://thehistoryofrockandroll.net/music-of-the-sixties-part-two/) (thus his overall influence (https://www.reddit.com/r/jimihendrix/comments/zyllxi/how_was_hendrix_so_influential/) or impact (https://www.quora.com/In-which-ways-did-Jimi-Hendrix-have-an-impact-on-society) on the music industry can just be downplayed), so don't put words in my mouth. Here's a link from a discussion (https://www.reddit.com/r/ToddintheShadow/comments/1c0fdms/every_x_killed_my_career_that_i_could_think_of/) that inspired me to bring forth this question to provide some context. The point about Hendrix (https://pedalpawn.com/blogs/news/did-jimi-hendrix-change-music-forever) was that John Phillips of The Mamas and the Papas in particular, once commented that when he came out (https://1883magazine.com/jimi-hendrix-had-a-massive-influence-on-music-history/), it according to him, signaled the start of the hard rock era (https://teachrock.org/lesson/introducing-hard-rock/) and the implicit need for guitar virtuosity in order to stay commercially if not at the very least, culturally irrelevant. Bands like (https://thyblackman.com/2022/12/29/african-americans-jimi-hendrix-and-psychedelic-rock/) The Who (https://en.wikipedia.org/wiki/The_Who) arguably benefited from the dawn of psychedelic (https://www.npr.org/2006/11/18/6491823/the-psychedelic-debut-of-jimi-hendrix)/acid (https://en.wikipedia.org/wiki/List_of_acid_rock_artists) rock despite not fitting into those genres.

I never said or insinuated that Jimi Hendrix (https://missionengineering.com/10-reasons-jimi-hendrix-is-the-goat/) was a Top 40 act unlike those other artists (https://thehistoryofrockandroll.net/music-of-the-sixties-part-two/) (thus his overall influence (https://www.reddit.com/r/jimihendrix/comments/zyllxi/how_was_hendrix_so_influential/) or impact (https://www.quora.com/In-which-ways-did-Jimi-Hendrix-have-an-impact-on-society) on the music industry can just be downplayed), so don't put words in my mouth. Here's a link from a discussion (https://www.reddit.com/r/ToddintheShadow/comments/1c0fdms/every_x_killed_my_career_that_i_could_think_of/) that inspired me to bring forth this question to provide some context. The point about Hendrix (https://pedalpawn.com/blogs/news/did-jimi-hendrix-change-music-forever) was that John Phillips of The Mamas and the Papas in particular, once commented that when he came out (https://1883magazine.com/jimi-hendrix-had-a-massive-influence-on-music-history/), it according to him, signaled the start of the hard rock era (https://teachrock.org/lesson/introducing-hard-rock/) and the implicit need for guitar virtuosity in order to stay commercially if not at the very least, culturally irrelevant. Bands like (https://thyblackman.com/2022/12/29/african-americans-jimi-hendrix-and-psychedelic-rock/) The Who (https://en.wikipedia.org/wiki/The_Who) arguably benefited from the dawn of psychedelic (https://www.npr.org/2006/11/18/6491823/the-psychedelic-debut-of-jimi-hendrix)/acid (https://en.wikipedia.org/wiki/List_of_acid_rock_artists) rock despite not fitting into those genres.

In your original post you didn't link anything did you? The acts you listed were top 40 acts and here's the question:

"Was it due to the arrival of Jimi Hendrix and psychedelic rock/acid rock, which signaled the start of the hard rock era and the implicit need for guitar virtuosity?"

I didn't say any of that you did. The answer to the question is clearly no, the as I said acts come and go in pop music all the time. The Cowsills had three big top 10 hit from late 67 to the spring of 69. The Classics IV had three top 10 hits, the Grass Roots had a nice 5 year run during this period, Simon and Garfunkel had two number 1's and a bunch of other top 40 hits. Cass Elliot had top 40 hits in 68 and 69 as a solo star. The Union Gap had six hits between 67 and the summer of 69, as the Captain and Tennille rose in popularity The Carpenters started to fade, that's the way of the business.