mikebg - you make a good point about probably the biggest downside of the BA program. Things change however when you go up in the ranks, Golds get additional award availability in Y and can secure seats if award seats are not available (similarly I think to LY), GGLs get that plus they can book 2 trips (or 3 depending on level) a year for up to 5 people in any cabin with avios by having seats released for them from revenue classes. Although I know little about your travel pattern, as an LY PL I think if you switched all or most of your travel to BA you would probably get to GGL (pm me if you would like to know more). The point you make about better availability is LY's only saving grace together with the fact that you can fly direct from TLV to several destinations.
However bearing in mind that with LY, points will expire within 3 years, if there was even less availability, it would make the program simply useless. At least with BA, I can keep those avios for as long as I like, maybe for a big trip once retired or when I can find availability on BA that coincides with time I can take off work. With BA you can hold on to a stash of avios for many years and whilst they are likely to devalue over time, it can still be the best option for many people.