Hmmm, haven't had one of these for a while. Mass produced basses are built for the masses and boutique basses are made for
you. Considering boutique basses haven't shut down mass produced basses and vice versa, both must have some sort of niche or a smart enough plan to stay in business. Despite what most guitards would say, bassists aren't a bunch of numb skulls. Although, these usually don't accomplish a whole lot since the arguments turn into "boutique basses are for bassists who have more money than common sense" and "oh yeah, well, mass produced basses are crapola".
The unfortunate thing about boutique basses is that they're price prohibitive to many players and a lot of the critique comes from guys who have never played them or they might have played a few and made their mind up about the rest. Boutique builders can be decent, good, pretty good, and pretty damn amazing. Their prices can be fairly affordable to something that might prohibit junior from going to college, which isn't to say that the best are necessarily the most expensive or that the not so good ones are the cheapest. In short, they vary by a LOT!
If you can go to McDonald's and have them hold the onions, why can't you do that with a bass??
I play boutique because I am not a bassist among the masses. The only way Fender is gonna make me a nice unlined piezo electric 6 string is if I become famous or drop more coin than most boutique builders would have charged in the first place.

So.....I can either wait for Fender to release the bass of my dreams or I can pay someone else to do it now.
My first bass was a Peavey Cirrus and I must say that it plays as well as most given boutique basses. Outside of boutique basses, not much comes even close. Although on a side note, it's always entertaining to hear that ALL basses can get low action, but I don't think I've met too many bassists who keep their action nearly as low as mine, but still are experts on my action.

Regardless, I'm still happy with the Cirrus series, but I can't get 'em with other pickups or electronics. Not that the electronics are bad, but I wanted other tones as well.
So, upon getting my boutique basses, the action on my CB and Conklin are slightly better than my Cirri, although the Rob Allen has slightly higher action to get that pillowy thump. Regardless, the necks are all extremely comfortable the low B strings (when applicable) are phenominal. Even though TB usually says that the Ray has the best low B, try something like a Curbow or my Conklin as the clarity and consistency can't be beat...without a Dingwall.
The sustain and resonance on all of my boutique basses is killer. Yes, this is the point where someone will exclaim that they want quick decay. It's much easier to mute than to hope for sustain that simply isn't there. The top notch construction coupled with the right strings and a good setup will often lead to basses with extreme consistency and no dead spots. On my Conklin, for example, my low B still sounds clear enough to play at the 15th position. Not many basses can do that!
Comfort comfort COMFORT!!!! Play a Rob Allen Mouse 30 or a CB Ball bass for a while and you won't want to go back! Both are extremely light and the CB feels like it belongs on your leg when sitting. My Conklin may be a pretty big bass, but still weighs less than some Fenders and Ernie Ball basses I've played lately. The neck profiles are set up in a way that they feel like it belongs in your hands. Back when my last band was playing for several hours at a time without breaks, the comfort really added up.
Tone? Totally subjective. While some may suggest that they're all high end zing that nobody would ever want to record, there are many different electronics options that can sound exactly like a Fender, have more low end, more high end.....or some that can sound like a Fender, get more low end, and high end if desired! Sure, you can upgrade electronics sometimes, but you don't always have the kind of room for some electronics. Sometimes the goal is to NOT sound like a Fender. It can be done.
The usual argument against 'em is that they're lawyer basses that often collect dust. First of all, never underestimate someone like a lawyer as a very determined personality is how they got where they are AND the same attitude is often applied to music. I'm a pharmacist by trade and have never had too many problems hanging with professional musicians. Guys who spend their entire day on bass have an advantage, which just means my practice must be THAT much more intense. My basses were getting played plenty when I was in my last band. Currently, many local musicians have been sidelined by a severe drummer shortage, so I can't brag how many gigs I have as a mass production bass vs. a boutique debate doesn't apply when there simply aren't good bands needing a bassist at the moment.