They could sound exactly the same- that would have nothing to do with the premise of this thread. The thread is about the quality of parts and finish- nothing to do with sound, feel, looks, or what suits one best as a player. The point was that it's okay if a boutique has the better parts- that doesn't mean it will have all the other stuff which is more important in the end and could exist in either a boutique or cheap bass.
It seems like a LOT of folks are reading the thread title and replying without reading the original post to see what it says.
Could also depend on what's considered "better" parts. Have to remember we're also dealing with artistry along with craft and equipment here.
Some players prefer, say, the old Fender vintage bridges over the badass or the hipshot or G&L. In that sense, the vintage bridge is a "better" part.
Some players prefer necks with no finish on them at all with the wood soaked with sweat. I would assert that that's probably an artistic interpretation of "quality", but I can't deny that it's valid.
Same with various different types of pickups and so on.
I think a completely objective judgment on "quality" of an instrument is going to be pretty elusive here.
What _does_ seem to be true in the boutique camp many times (but not always) is the presence of the claim that the "boutiqueness" of the instrument usually makes the player better.
But this is demonstrably false in most (but not all) cases simply by having the claimant play a variety of basses and listening to the results. More often than not, my observation has been they sound the same on the "cheap" or "crappy" gear as they do on the stuff they spent half their estate on.
I include myself in this result, tho my level of technique and musicality is in my judgement somewhat below average and so probably not very typical.
Now, if you alternate other aspects such as fit to the player and desired tone, you can and do observe a difference. I.e. the player will sound better on the more ergonomic bass because his/her hand isn't being crunched up, or not having to hold the instrument or etc.
I'm in this camp too - I sound and play noticeably better on basses that fit me.
But only in exceedingly rare cases have I ever heard any of the boutique guys sound any better at all when alternating on the "boutiqueness" only.
So I can't go along with the "boutique" == "better quality" claim right off the bat, the evidence I've heard so far just doesn't support that.
In my particular case I have my own opinions about quality, but those are more artistic judgments (i.e. the hipshot bridge on my carvin I'd consider better quality than a Fender vintage bridge, I think the woodworking on my carvin is better than the typical woodworking on a Fender, etc). At least with my level of playing skill, I can't really demonstrate the truth value of that claim, tho. So I can only say it's a matter of personal opinion.
LS