The math now is perfectly simple.
With the reduced rates for tier points and avios, the only significant difference between BA and EZY on s/h economy now is the lounge access.
If the difference between the fares is less than one would spend in a café before a flight, then one should stick to BA.
Since I see that many people are not particularly gluttonous in the lounges and sometimes basically sit and enjoy their laptops with a cup of coffee I can understand that a part of BAEC, who primarily fly s/h economy, will move to a real LCC.