I think of a couple of things:
1) Although premium loudspeaker companies may use drivers sourced from large volume driver makers (Scanspeak, Seas, Focal, etc.), they usually work with the design teams of the driver manufacturers to come up with units to their exact specification. So it’s not just an off the shelf Seas 1" tweeter for example, it has been tweaked. And then the speaker manufacturers tweak the drivers further once they get them in house to perform to their design objectives.
2) There is significant cost in utilizing designers who have gained in wisdom and experience over their years in the business. Just like in any other business, this experience and ’tricks of the trade’ can be invaluable in how the speaker ultimately sounds.
3) There is a significant amount of listening and measurement to produce a certain sound and measurably flat response. Harbeth, Spendor, ATC, PMC, to name a few - use state of the art development software and measurement equipment to achieve ’studio monitor’ requirements. (Which may be different than their ’consumer’ goals). And they have DECADES of experience working with the top European driver manufacturers as materials science has advanced. The PMC PB1i which I own ’appears’ to have a pretty basic 3" Vifa dome midrange. But PMC has tweaked the driver and designed a crossover with very specific parts and slopes to achieve a sound and performance that mates beautifully with their goals to achieve a flat power response and even output for all of the drivers in the speaker. To say the speaker uses a "$60 Seas tweeter and a $100 midrange" totally misses the point. And to say that an $800 ATC dome midrange would be "better" in that design also misses the point. Such a driver may be very inefficient, or have to be driven very loud to achieve it’s optimum sound, etc. Which may not be the goal of a ’consumer’ speaker that needs to sound great at low/all levels.
My advice would be to find a speaker that pushes all of your buttons. There are lots of speakers that are "ok" - but we know in this hobby that "just ok" is ultimately unsatisfying. Probably sooner rather than later. There are some exceptions, of course, but the speakers that are at that next level (which for some starts around $5k/pair) - are probably designed by experienced professionals with industry manufacturing relationships and significant [design and testing] resources. Not by someone that just purchased crossover design software and will buy his drivers from Madisound or other distributor. Good luck.