For a start, the taxes should be identical - if, as you are implying, FR are not charging the same taxes as BA did, perhaps the newly formed Customs and Revenue department should investigate why FR has a shortfall?
Secondly, BA always had low fares. BRS to DUB's lowest fare was, in fact, £23.50 return when I was in Sales and Res 5 or 6 years ago. - it just wasn't advertised because we only had a couple of seats on each flight at that fare and the Advance Purchase and non-change restrictions made it unsuitable for the business traveller.
However, you business travellers wouldn't tolerate "non changeable, non refundable" from Auntie BA, yet you quite happily have welcomed the restrictions with Sleazy and Liar Air!
Lo-Cos are a trendy break away from the mainstream carriers - without the misfortunes of 09/11, they would have gone nowhere!!!