There seem to be three categories of people who post about custom builds from smaller boutique builders:
1. The no-research nightmare stories. They find a website, talk to the dude, throw some money at him, then start doing their research. Turns out there were already threads, posts, and receipts about issues but these people either are new to the idea of custom orders or have money to burn without any concern on return. Now the whole project has gone to hell and they are one more voice shouting about how much X builder sucks.
2. The pile-on guys who either have one experience as category #1 or have never actually gone through the process at all. They will tell everyone who will listen how much boutique instruments are a waste, how every luthier is a crook, and how their 1992 Fender P-bass with a Dead Kennedy's sticker can outplay any Fodera. They are in every thread and super vocal about their opinions.
#3. The happy customer. Whether they are pros who need quality gear or hobbyists with day-gig money to invest in nice things, this is the category of folks who do research, plan ahead, understand the biz and requirements of custom instrument orders, and mostly walk away happy. Sure, no industry has a 100% approval rating, but it's pretty rare that this category posts stuff like "I gave X $5K and all he sent me was a plank with some googly eyes on it and an invoice for $2,500."
A big part of the issue, in my opinion, is that people don't understand WHY anyone would order a custom instrument in the first place. If your old P-bass does the trick why in the world would you pay $3K and wait two years for a new bass? It doesn't make any sense to them, so they are very vocal that it should not make sense for anyone else.
When I started researching custom and boutique instruments (Fodera, Alembic, etc. and then the luthiers who build boutique instruments but aren't as well known) over 20 years ago I talked to a lot of players from all over the world, from hobbyists to Grammy winners. I came away with two reasons to look at custom boutique builders, and I think it still applies today.
1. What you want doesn't exist on the market. Maybe you want an unusual scale length (more common today than 20 years ago), uncommon electronics, or very specific dimensions that nobody produces en mass. For example, my 30" 5-string tenor bass with 2 magnetic pups, a piezo bridge, and a dozen control knobs/switches. You can't find that at Guitar Center.
You also have people who know EXACTLY what they want and close-enough just won't do it. Neck dimensions, string spacing, finish, even types of fret wire. Whatever it is that you are after, you have identified it, looked at the market, and nothing checks all your boxes. It's time to talk to someone who can build the thing you want with every feature.
2. The quality-to-cost ratio is worth it to you. Sure, you can play and gig and even make a living with a cheap instrument. And maybe you can find a stock bass for $800 that feels pretty good, even compared to a $2,000 build. But if you are playing hundreds or thousands of gigs/sessions, even a 20% increase in feel, ease of play, or tone can be totally worth the expense. I had a bass built that sounds fantastic and I've received compliments on it's tone for 20 years. Over those years I have had bands specifically request that bass and it's paid for itself many times over. For me, when I was gigging 4+ nights per week and developing arthritis and other health issues even a slight increase in playability and ease was the difference between working or taking time off.
Outside of pros you also have people in this category who just have money to spend and appreciate nice things. Sure, they COULD play on a MIM Fender, but they are financially stable, enjoy the sound and feel of a boutique instrument, and to them the value is worth the cost. No different from people buying fancy cars, expensive office furniture, moving into a big house, or investing in their hobbies with tools like quality golf clubs.
So, no, nobody NEEDS a boutique bass just like nobody NEEDS a nice car. But for people who know what they want, have researched the market, and know what to expect from a custom build it makes perfect sense to go the boutique route.