I think it depends on one's philosophy and real needs.
Based on the session professionals that I often work with for ad projects, I'd say there's really no such thing as a "must have." Plenty of players have their own preferences and don't feel a need for much else. Then again, lots of players feel they have to have all bases covered, so I think it's a matter of whichever guitar 'belief system' one subscribes to.
I have worked with serious pros who will only use one guitar model. So one just never knows.
Point well taken......I am inclined to look at it in a bit different light. A good many of us (speaking at least of myself) have less than "pro" needs for different instruments. But we WANT (and hopefully can afford the cost and potential marital grief") of having multiple "toys" to choose from. In that context, the "basic food groups" (to many people) fall into the Tele, Strat, Les Paul, ES-335 camps. As I recall the very earliest ads for PRS featured the ability to get both "Strat" and "Les Paul" from a single instrument. At that time, such things as coil splitting were far less common.....So, sure, there are some compromises (scale length and other things) but a GREAT step forward......Got my first one (CU 24) in 1990.
If I dealt more with reality, I would realize that I SHOULD be able to do most all of what I want/need to do with a single guitar......Okay, to my taste, the modern PRSi, with new pickups and finishes and all else, do a better job for MY tastes than the old ones. But the point remains the same.
But how many times have we heard, "But only a Les Paul IS a Les Paul?" If I pickup up a ME I (for example), it is different enough from the "classic" PRS (let us say CU24) what with the thicker body, greater weight, newer pups, etc that it gets me close to "that" LP sound I hear in my head. IMO, my Huber Orca 59 DOES have that sound (yeah, a purist will argue it has a 25" scale, so it is not "right") even more so. (FWIW, I have never played a "real" Les Paul that was anywhere near as good----The '56 goldtop I let go a LONG time ago was, of course, something of a different animal, but I have had a ton of others come and go too). And I am of the impression the new PS models ("Hammer of the Gods" and its siblings) tread that same path.....Meaning as good as most, better than very many, "real ones".....Those who know much better than me seem to insist that not every original "burst" is "magic" and not every original PAF is definitively better than anything being made today.
For ME, I can get close enough with a NEWER HBII (modern pups, etc) to get all the sounds anyone of my limited ability has any right to get, with the bonus of some "acoustic" blended in, etc.....But when I DO pick up the Orca, select an "M" input and crank it for a Gary Moore tune, I KNOW (and feel) the difference. (Now if my VOICE could also get his sound, that would be something my mates would appreciate!) Fortunately, I can get away with having both guitars (and more, besides). So, to me, "must have" is a very relative thing.......It makes me happy to be able to lay claim to both an HB II and a (sorta) Les Paul.
Real "need?" No. Real fun? Sure!