What will it take to convince they need test server?

The LFP tools design could have been easily seen as useless with even a small test-group of people.

The login-issues could have been ironed out before letting it affect so many players.

New radical gameplay changes could be tested harmlessly so that SE wouldn't be forced to take babysteps in improving the overall game design.

Please make a test server it doesn't have to be international if translating issues costs too much just make sure amateurish game design flaws like LFP tool don't make it into the game as it makes the whole product seem cheap.

They're wasting a huge amount of developement time and money by trying things in the real game because they need to be polished in detail before they even see if the feature works or not.