In a nutshell:
The current model catches plenty of bugs, there are lots of people testing things and getting their opinion on design aspects of new features for Frontier to take on board such as what's frustrating, what's enjoyable, what doesn't work as intended, what doesn't really mesh well with it's associated parts of the game.
Some things in 2.1 weren't able to be given Feedback on because Frontier never exposed beta testers to it, Frontier made a conscious decision to mask the live state of engineer recipes and access unlocking requirements for example, and had everything just require 1 unit of Fish and then added a commodity market to all engineer stations that sold Fish. Until Beta 6 they also had Engineer modifications that supported enhancements have a 95% chance of getting a enhancement as well as ramping up other aspects of modifications only tuning down closer to what they intended for live in the final beta build... and that was Frontiers decisions based on what they wanted focus put toward.
There was even mention in Beta of problematic acquisition of Meta-Alloys long before 2.1 went live, but as Frontier had made a point of saying they had disabled various things in Beta to hide some secrets that would be reveal themselves across 2.1 live, it was impossible to tell if the Meta-Alloy acquisition was a bug or intended pending changes that Beta testers weren't given access to, and Frontier to my knowledge made no effort to chime in or clarify if it was a bug or not... so the whole thing ended up getting ignored and then 2.1 went live, Farseer needed Meta-Alloys and none were to be found.
The beta forums are also archived you can even go over and read them to see the bug reports and discussions there so there's no need for all this made up "Well it released bugged so the problem is the testers and testing environment! Cus I made connections and just ran with them as facts!".
Frontier have a looooong track record with Elite Dangerous of playing the "Least amount of development investment for acceptable return" when it comes to responding to issues and resolving things, half the time it seems driven by what they intend to do in 8 months time, seeing it as perfectly fine to have something horribly broken or partially functional live because in half a years time or more they'll be doing something that replaces that problematic content.
You only have to look at 1.x where we went multiple months live with any mission that involved being presented with an enforced counter-offer when running the mission would break the mission and make it impossible to complete either way, and practically all combat missions involved enforced counter-offers.
Or 2.0 with the mission system where any and all 'Mission Specific' items were being failed to be registered as acceptable items by the mission system so anything to do with collecting items for a mission was impossible to complete, and Frontier left it like that for almost half a year from 2.0 to 2.1. Only taking measure to remove said missions from live when they announced 2.1 was going to be delayed by around 2 months.
Or let's look at the "Death spiral" NPCs that would frequently stop stationary mid-fight and just spin on the spot... how long exactly did Frontier leave such behaviour in live as the recurring quality of AI behaviour?
And also with 2.1 there's the whole "Planets outside the bubble won't have POIs outside of a few cases" change. Yet flying outside the bubble I've come across quite a few POIs, what has changed changed however is that outside of the bubble your ship scanner no longer displays POI markers when over 2KM... not even element sources. But land and use your SRV scanner and you'll still stumble across the occasional find that if you take off in your ship your scanner will swear doesn't exist... this wasn't quite so possible to test in Beta as many people were reporting that trying to go out of the bubble into more distant system would just cause disconnects, myself included as my carried over save state was 2,000ly+ from Sol, and trying to leave the system I was in always caused a disconnect in Beta so I ended up resetting my save progress which was good overall as it meant I could touch on the 'fresh start' experience of 2.1.
So Frontier being selective about what they fix, what they consider a fix and what they just shrug at and let go into the live game should be no surprise to anyone, it should also be trend everyone is familiar with.
2.1 Beta participants caught lots of bugs and problematic aspects, Frontier weren't quite so bad as in previous betas and this time actually did quite a few bug fixes based on what was reported and reactively disabled some of the missions that were reported as bugged, where as before they would have just rolled them out live anyway without a care in the world..... but that isn't to say that everything that rolled out broken or has issues in 2.1 wasn't picked up and reported in Beta.... making that assumption is both short sighted and incredibly ignorant especially as the Beta forums are archived for anyone to check out as mentioned before.