I've had decent success with switch hitting with and without abp. A flexible combat approach is often rewarded in my experience. I've seen drifters at play in my games and they've filled that role reasonably well. The premise of the thread though I do tend to agree with. Gunslinger could use some help but I don't think it's as abysmal as people tend to think.
Funnily enough, I've had the exact opposite experience both personally and watching others attempt it.
The closest I've come personally was a MM Rogue, adjusted so that repeated RK checks still used the base RK DC for the purposes of my ability. Early on I ran a thrown weapon/melee hybrid build, but eventually I just went full ranged, because using a bow ended up being just better, as I was the only character with any ranged potential. Full Rogue parties are wild.
If we hadn't decided on playing the same class or would've had to play vanilla MM (yikes), though, I just wouldn't have used the MM. I would have used an actual ranged class, because my relatively small added melee contribution as a MM would be worth less than the increased ranged contribution of a specialist.
And that is how it always goes in my eyes, at least when you have the opportunity to build a well-rounded party. The occasional increased contribution in edge situations isn't worth the switch hitter doing less than a specialist most of the time. Often substantially so, even. Being able to switch hit always involves heavy compromises that others simply don't have to make.
Having a backup weapon in case of shenanigans is useful (especially a ranged weapon as a melee specialist), but that isn't really switch hitting.
Funnily enough, I've had the exact opposite experience both personally and watching others attempt it.
Probably the best Switch Hitter build in 2e I've played was a 6th level Human Ranger. They were a guest PC (the party got split cause of portal-eqsue shennigans) and they had an Arquebus for some crazy high damage spikes (Pretty sure they still have the most damage dealt by a character in my group w/ 72 thanks to GB, Fatal & Precision and we're level 8 now) as well a Bastard Sword & a Steel Shield for Melee. Both the Sword & Gun had +1 Striking runes. Their feats were something like:
H - Gravity Weapon (targets you so it increases the damage on both weapons even when you switch)
1 - Animal Companion (To keep enemies at bay and help flank when I swapped to melee)
2 - Quick Draw (This was pre-remaster so swapping wasn't an option, but I could drop a weapon and then quick draw)
4 - Running Reload
6 - Mature Companion (To keep up with PCs)
They also had a bunch of alchemical ammo (Life Shot for one literally saved a real PCs life) and some random elemental ones. Once set up, they would usually try to get above enemies and the economy basically was a mix of strike, running reload, command the Animal until they got into Melee then quickdraw either Sword & Board or 2H the Bastard Sword if I had the extra economy for it. Or Reverse the order if they started in Melee and I found an opportunity to swap to Ranged.
All the above is to say that this is what I'd call fun still, since I felt just as effective in melee as in ranged, even if it doesn't meet your definition of Switch Hitting. Though I'd point out it'd probably be even better now with the new interact rules to swap weapons since I'd have an easier time switching back (no picking up weapons). Also that my current Fighter w/ Gunslinger Dedication is much more in line with the above play loop, save his Gun Sword is no longer his main weapon these (it's his backup).