...the folks doing the play testing were for the most part truly veteran players. They have been around for quite a while, and didn't just read about some "old school" builds they also learned how to use and counter those lists.
The simple reality is that most people do not play at a top level, and the overwhelming majority of people do not approach the aforementioned "skill ceiling" of their lists, even if they play competitively. So play testing amongst "truly veteran players" creates an interesting set of results. From the standpoint of highly skilled competitive players, things may get through play testing being "not broken" because those players truly have the skills, both in list-building and in flying to employ strategies necessary to defeat the upgrade du juor. They can use things with a higher "skill ceiling" to their advantage. And so on the level of high end competition, all seems well.
For top tier players, TLTs may very well be balanced. They hit the "skill ceiling" when using them and run out of places to incorporate their skill. They waste it, and so for them, TLTs get dragged down a peg. That doesn't necessarily equate to good for the game as a design element element however. 9 out of 10 players will not hit the skill ceiling with any list.
Take two average players of equal skill. One flies TLTs, the other interceptors. It doesn't matter if the TLT ceiling is low and would be limiting to a top player, neither player here is going to run into that disadvantage. The downside of skill ceiling is nonexistent. The upgrade du jour will affect casual play, small local tournaments, etc and gradually reduce in effect as the amount of competition rises.
Now, the game should be balanced with competitive play in mind. However, it behooves the designers to, I think, be very cautious about upgrades/ships with low barriers to entry, but a significant impact on the meta (such as TLTs). Even if they have a skill limit that keeps them from taking down regionals and nationals, in a game of equally skilled average players, they will seem dominant. These types of upgrades affect a lot of players and will result in a lot of negative player experiences. I've railed about NPEs numerous times - it is almost irrelevant if the thing in question is unbalanced or not if it creates a NPE.
Two players of equal skill, and one with a pre-nerf phantom takes down nearly the other guys entire list. Fat turrets flying in circles - all the nuances and tiny advantages are lost on the majority of players - it appears to be a dice fest. TLT spam appears to be a wall of mostly unavoidable damage. Highly defensive ships that simply cannot be killed by another single ship (I'm looking at you Corran Horn with R2-D2 and evade). All result in NPEs, and so while they might be competitively balanced at the high end, these things the types of things that are better avoided than included.
Long story short - High Impact upgrades should be designed to be high skill (high skill floor). Upgrades that have high impact with a low barrier to entry will cause a lot of headache, whether they are balanced or not.
Edited by GiraffeandZebra