I've only flown Y and PE/Elite, so that's what I will discuss.
All airlines are obviously getting worse in the back of the aircraft, but I haven't noticed as much decline with EVA when it comes to soft products / service in comparison with other TPAC carriers.
I feel like ANA's food has really gone downhill big time. JAL has hired a lot of foreign FA's who are not as professional. UA and AC remain stably mediocre.

BR has better food than any of those airlines. CX and SQ are the only TPAC airlines with better overall soft product in the back, although JAL has hard product and ANA has better service but worse food. The only decline I've noticed in BR over the past two years is that the PE dinner salad has become significantly cheaper and no-frills recently.