There have undoubtedly been some poor 2005 champagnes.
I think it was Tom Stevenson who reported that the vintage had the unusual quality of causing some bunches of grapes to rot from the inside out. As they don’t normally do that, lots of bad grapes escaped sorting and made it into the crush. Especially diligent producers spotted this and took appropriate steps to rectify matters, so there are a number of producers who made good wines in the vintage.
Bollinger has been through a spell of adding no sulphur at bottling time - the resulting bottles have been distinctly variable in their maturation as a consequence. I understand that having introduced jetting, the bottles are now a much safer bet. I stopped buying them - a great shame as Bolly was a favourite of mine.