I'd argue that ruling out a "playstyle" which ignores 90% of the game's systems in favor of mineral/alloy spam (in 2.1/2.2 respectively) is actually a good thing, both in competitive and casual settings - in the former case it raises the skillcap immensely by making the game's complexity actually come into play, and in the latter... well, being removed from the game by 2215 isn't particularly fun for anyone involved. In the end, making Stellaris play like something it's not - a fast-paced RTS - will never work no matter how hard you try.
Also, this is once again a people problem, not a numbers problem. If the player in question joined a game advertised as competitive and didn't play competitively, then yes that's entirely their fault. However, if said player joined an alleged casual or newbie-friendly match only to get pubstomped, something somewhere went horribly wrong.
the problem currently is that prior to 2.2 you had SEVERAL competitive builds. However in 2.2 you only have ONE competitive build/playstyle which everyone agrees upon.
The casual vs competitive players issue is another topic entirely.
This build just highlights a few overall issues with stellaris. Like not being able to design your own star bases. M slots, circling, and damage spread make star bases terrible at fighting against corvettes. Defensive stations would be much better, but their cost hasn't been adjusted to the alloy system (to be honest almost nothing has been adjusted to the new eco system, mining/science stations/discovery events/"space" hostiles).
Stellaris is a 4x strategy game. So rushing should always be a valid choice of play. In the current literation it is however the very best choice as teching and expansion have been severely slowed down, yet again, in 2.2
Even in Civ you have much more valid options to play in a competitive MP game.
Who are you doing pacts with if everyone are genocidal maniacs?!?
To be honest I don't think many strategy outside the ones with aggressive nature are very viable in competitive MP unless you happen to spawn in a game where you manage to get a few people near you that also want to cooperate which seem unlikely in this environment. So luck seem to be the biggest factor for more peaceful strategies, most good players don't rely on luck though.
Not everyone play a "genocial" maniac. A warmonger empire is still heavily structured. Many players do rush but only a couple manage to transition into a well managed mid/late game empire which is capable to taking on crisis solo. You will still need pacts between players, research agreements and mega corp buildings are always nice to have if you have a 100 pop planet at year 20.