I always thought, obviously incorrectly, was that session musicians would be hired on their ability, on their efficiency and reputation - not on whether they own the right Strat/LP with the right PU's. I have no issue with turning up to a job with a strat type, LP type one with Humbuckers and maybe one with P90's, semi-hollow/hollow type if you are not given a heads up - same with taking an Amp or two - one for cleans and a one for gain but to be told it has to be a Gibson LP or Fender Strat for example doesn't make sense to me. Again not saying this doesn't happen but that it just isn't reasonable as there is probably a wide range of tonal variation across 'Gibson' Les Pauls as there is between the brands that make Les Paul types. My 594 for example could be the 'LP' type tones with more clarity and articulation that does a song justice compared to be forced to bring a Gibson that gets a bit more muddy just because of brand prejudice. To reiterate, I cannot see any issue with being asked to Bring a Les Paul or Strat and then turning up with PRS versions because that's the instruments you own and feel most comfortable with without being sent home because you didn't bring Gibson or Fender but don't understand being told or expected to turn up with specific brands when a 'brand' can have just as much variation in tone as there are between different brands - after all, isn't it the sound they want not the pictures....
I do session work - certainly NOT at the level of what Les is talking about. You are hired for your ability. I broke into the local session scene because I am a versatile player with some reading skills, have a good ear, good tone (vibrato, note intonation), and good gear. However, I work in small studios - often just glorified home studios that happen to be in treated storage units - like I said, NOT at the level Les is talking about....
Anyway, when I started I still had a lot of other guitars and only a couple of PRS'. Even though it was all low-level/low-buck stuff, I still brought several guitars to a session. If I was coming in to do a song (which sometimes I wouldn't know) that would "normally" have a strat sound, then the producer and/or artist would expect to hear that sound. Not something "close". Having "better" guitars (PRS), it was frustrating because a producer and/or artist would rather have me play an entry-level American Strat over my PRS Custom 22. Oh well, their vision/song - not mine.
As a session player, I have to remember that instruments are colors on a paint palette. While a 594 can deliver Les Paul "like" tones, it still does not sound like a Les Paul. I was hoping it would get me closer when I got mine - and it did - but it is still clearly NOT a Les Paul. It's still missing something, so if I need that color (the Les Paul sound) in my palette, then I NEED an actual Les Paul. If I come into a situation where a producer requests a Les Paul, and I don't have one, then I am not doing the job expected - which is provide the sound the producer and/or artist is looking for on the song. I am being paid to do a job, and while I could say that my 594 is les Paul-ish, at the end of the day I have the wrong tool for the job....the wrong shade of red, so to say.
Now, I am in a lucky spot. I do enough with the local "producers" that they pretty much leave me alone. I deliver. I always ask up-front what they are hearing/wanting for the song. If the producer KNOWS guitars they will say something like:
"Les Paul into a Marshall, played like Johnny Thunders."
That gives me something VERY specific to attain. In all honesty, I am gonna rent a Les Paul and a Marshall. That has only happened a couple of times - not enough to justify me actually buying a real LP or a Marshall.
If the producer just says something like:
"Ummm, I want the guitar to have that Jimi Hendrix feel."
That tells me I have a little more room for interpretation on gear. The producer is looking for a vibe, not specific gear. In that case, I'll bring a couple different guitars that I own - which at this point are all PRS (except a custom built Esquire). I'll pack my EG3, my Brent Mason, a Paul's Guitar and maybe the Vela. All of these are guitars that I have comfortably played Hendrix/SRV songs on. Once at the studio, I'll quickly play the part on each guitar and then narrow it down from the play back.
However, the last couple sessions I did were the kind I don't like. I had an email exchange with the producer where we discussed the track and what they were looking for me to do with the track. A couple days later, I got an email saying the stems were in my cloud and I dropped them into a Protools session, recorded all my parts as DI'd parts, uploaded back to the cloud, and got paid via PayPal. I hate those sessions because there is no guidance or input from the artist or the producer. I mean, I am more than capable as a player, but what I might choose to do if it were MY song could be very different if I stumble into a "grey area" while tracking. What I DO like about those sessions is, that as long as the sound is "right" I can be less "accurate" regarding the guitar...like using my 594 instead of an actual LP.
Pretty long here, but I hope that kind of explains it from a session player's (well a fake one anyway, lol) perspective.