I understand the want for a higher end mtb. I teach mountain biking as a side gig, so I spend a lot of time on my mtb. It has to be fun, durable, comfortable, and good enough to not be slowing me down when I'm with clients on much more expensive bikes. I should point out, I
do not race, so out right performance of a bike is less important to me than reliablity.
I'm going to suggest that you can get a bike that will do everything very well for $1500 or so. Here's how:
1 - Don't get this years model until it is heavily discounted by the distributor (usually end of June, bike shops can order in the exact model you want for 70% list or less). Ideally get last years model (50% off). Despite what the magazines say, most bikes don't change a lot year to year.
2 - Following on that, I'd go with a mid range drive train. Shimano Deore or SRAM X7. These are both pretty much the same as the previous generation (last year, maybe two years ago) higher end parts. They aren't as light as the current higher spec parts (use cheaper/heavier materials), but are rugged and reliable.
I prefer the feel of the SLX shifter to the Deore that came on my latest bike, so I picked up a set of SLX shifters on close out. But once I got used to the 'basic' deores, they were good enough, so I've never put my SLX shifters on. Same goes for brakes. Two year old Deore brakes (M485) are as good as the Juicy 7s from three years ago. I know, because I swapped my "higher end" juicys on, and was dissapointed to find exactly the same perforamance and feel.
If buying full suspension, do your research on the frame. If the frame uses a linkage design that negates pedalling influences (Horst linkage, or a linkage driven single pivot 3D link, Magic Link, etc) don't pay extra for a pro-pedal rear shock. The suspension design is already doing 95% of the work the 'pro-pedal' is supposed to. Save $200 by going with the lower end shock.
The exception to all this is front forks. Forks are worth the extra money, you can definitely feel the difference between a $200 fork and a $600 fork. The good news is JensonUSA and other websites often have closeouts on last years models for as much as 50% off.
Remember, that wth the possible exception of Carbon edition frames, the frame on a $1500 version of a bike is the same as the $5000 version. It is only the part spec that changes. So buy the lowest part spec that will give you good reliability, and then upgrade the parts you care about.
So, find a good frame you like, buy it in a lower-mid trim (not base, you do not want an Acera drive train), and use the saving to upgrade only the parts that really matter to you. Buy close-out or last years model of everything. It isn't hard to get a bike that rides like $3000 for half that.
I will agree that the super high end bikes ($3000 is not in this range) are designed specifically for certain companies but frames and componentry come from the same third party vendors and are assembled by the same employees for lower and midrange bikes. But feel free to fund the big bike brand's Tour de France teams and multi million dollar marketing campaigns.
I recommend you speak with some designers at Devinci, Intense, Banshee, Rocky Mountain, Santa Cruz, Norco, Marin, and many many others. They design their own frames. Many (such as Devinici and Intense) even manufacture their own frames. Those that don't (like Banshee) most definitely do design their own frames. And yes, many frames have similar geometery, but a quarter inch difference in a pivot position changes a bike from perfectly smooth to P.O.S.
Yes, components come from Shimano, SRAM, and others. And some companies do use Tawainese designed frames (Opus mountain bikes were and maybe still are sourced from a provider, Opus deals with the component selection, assembly, and distribution). But in my experience the vast majority of mountain bike frames sold a local shops are designed by the company with the the logo on it.