Why is this thread so long and mostly arguing about nothing lol? All of this information is readily available on the internet and easily researched.
80s hard rock and metal is very straight forward. Back then, most guys were either using a cranked JCM800 with an SD-1 or other boost (Rat pedal, etc.), a Soldano SLO-100, or a Mesa Boogie Mark III or IIC+. Marshall Plexi's were used too, but they needed more of a boost with the boost/OD pedal than the JCM800, so you'll usually see more of the JCM800s used by those 80s players. ADAs were also used, but it didn't come out until 1987, so that's towards the tail end of the 80s and wouldn't explain everything everyone was using before it. With the Boogies and Soldano, you didn't need a boost like a JCM800 does since they had so much gain on tap. Towards the mid to late 80s, everyone was doing the LA session rack "fridges", so they needed amps that could fit in them. Those were usually the Boogies or ADAs.
In the early 90s, the Dual Rectifier came out for the hair metal guys, but since hair metal died with the grunge movement, they were never really used for hair metal in the studio. They were used live however by 80s hair metal players who were still touring.
Jason Becker, Paul Gilbert, Michael Angelo Batio, John Sykes, EVH, George Lynch, Warren DeMartini, Reb Beach, Randy Rhoads, Neal Schon, Jake E Lee, Steve Vai, Yngwie, Satrini, etc. all used multiple of the above amps at some point. Back then, there wasn't as much to choose from, so they used what was around. There were no Diezel VH4s, Friedmans, Engls, 5150s, etc. A lot of their sound, especially fast alternate picking, and legato, came from their technique like their clean pick attacks, not the gear they were using. This is easy to figure out since most of them used the exact same gear as stated above, but sounded completely different. Ex: Yngwie sounded nothing like Randy Rhoads or EVH or Lynch, yet they were all Marshall players. A good example of this is the Hear N' Aid "Stars" song from the 80s. There is definitely a Marshall in the video, so you could probably guess that it was used for a lot of the track. It was released in 1986 too, before the ADA.
The hardest part of the 80s sound to replicate is really the tri-chorus/clean chorus sound. Usually clean parts by Michael Landau, Dann Huff, Michael Thompson, John Sykes, or Lukather. That required a lot more effort, like rack units consisting of delays, reverbs, chorus, compressors, etc. Even today, replicating that part of the 80s sound is a little more involved. The distorted rhythm and lead parts are actually much easier. Here is a good video on that sound.
As for Axe FXs and Quad Cortex's, they are fine. Huge stadium acts are using them like Metallica, Ghost, etc. I have an FM9, but I personally think for the average player, they're hard to dial in consistently based on the venue, PA, your band, etc. so they would be better served with a lower wattage tube amp. Its easy to have them sound huge and consistent when you have roadies, have sound engineers, and know the venues you're playing. But generally, they get a bad rap and don't sound great by the average player. They're great for recording too though since its already a finished, processed sound.
Players way more technical than the 80s guys are using Axe FXs/Kempers/Helix/Quad Cortex to great effect these days. Players like Tim Henson, Scott LePage, Tosin Abasi, Plini, Jason Richardson, etc. These guys are way more technical than a lot of those 80s players. Most of them are also using far less gain then those 80s players too, and at far quieter volumes. So saying its down to tubes, no tubes, or just gear is not correct.
Another weird thing about eighties hard rock/metal is that a lot of the guitar parts were not recorded by band members. Let's take Whitesnake's 1987 album. Adrian Vandenberg and Vivian Campbell appeared in the videos, but they had very little if any input to the album, which was mostly written/recorded by John Sykes, but even he did not record the solo on the biggest hit on that album; namely, "Here I Go Again." Sykes could not come up with a workable solo. If legend is to be believed, Dan Huff came in and recorded the solo in one take.
Your info is all wrong on this. Sykes (along with the rest of the band) was fired before completion of the 1987 album. Supposedly he had or may have recorded a solo for Here I Go Again, but its never surfaced.
Also, Dan Huff didn't record the solo to the well known version of Here I Go Again, Adrian Vandenberg did. That's the only solo he played on the 1987 record. Dan Huff recorded the solo to the 1987 "radio" version of the song, which isn't the version of the song that became the mega hit. The Radio version is the version that omits the synth and vocals lines in the beginning.
Also, most of the hard rock/metal guitar parts of the 80s WERE recorded by the original band members. Whitesnake is a special case because David Coverdale goes through musicians like toilet paper. Players back then could play, so there wasn't a need to bring in session guitarists. The session guitarists were mainly used for solo artists (i.e. Michael Jackson, Peter Cetera, Richard Marx, Whitney Houston, etc.). But those acts weren't "hard rock/metal." Drummers are a different story, but the guitarists in the 80s pulled their weight because much of the music was so guitar driven. The only good example I can think of is Tim Pierce being used for Bon Jovi's "Runaway." And there is also a rumor that Slash didn't record some of his parts on Appetite for Destruction. But those are rarities.