I can understand the frustration, but as someone who often criticises BA pretty harshly myself, I'd say that nothing in the experience that you highlight is either BA specific or even out of line with the vast majority of the industry.

That part is quite simple to answer. The put flights for sale nearly a year in advance because basically everyone else does. If an airline chose not to do it, effectively, it would leave the competitive field wholly to all of their competitors thereby shooting themselves in the foot. It would be absurd of them to do so and it would thus be unreasonable, I think, to expect any airline to not put flights up for sale until it has finalised its timetable.

On that front, it is simply the case that absolutely zero airline in the world knows for sure its timetable a year ahead. Typically, the timetable available in, say, September 2026 as of October 2025 will be largely based on the September 2025 timetable, but airlines start fine tuning their schedule about 6 months ahead of time (hence current threads on flights just discontinued in the summer season 2026 which starts in late March) with one or two follow ups and notably reallocation of equipment based on past form, new bookings, rotations, etc. That is for European airlines, including BA. If you were to look at US airlines, literally, the changes and updates happen almost every week and all the way till about 3-4 weeks before flight time. Why change 6 months or even 3 before a flight? Well, because the airline industry is in constant flux. International affairs, exchange rates, politics, etc change expectations of passengers behaviour all the time, frames can be received or delayed, break down or get repaired, there are hundreds of possible combinations for rotations that can be modified and optimised based on everything from frame availability to changes in workforce and so on.

So like it or not, BA will keep selling you tickets almost a year ahead and will keep refining their timetable ahead of and close to time because every penny matters and because everyone else does the same - don't believe me? Proof is in the pudding as the first change you experienced was not by BA but by QR, an entirely separate airline. Incidentally, one thing which is BA specific is that they are on a fast path towards reducing their F offering and updating frames to do so with more and more three class aircrafts, so by and large, the risk of F flights losing F in one of the changes is non-negligible. QR are also all but discontinuing F and AA are discontinuing it progressively but entirely so since the most frequent combinations of flights you can purchase with BA are BA, BA-AA and BA-QR, well, you do the maths...

Well, again, that's straightforward. Airlines will not rebook you on a different airline because of their own time-limited schedule or equipment change, full stop. There are different rules if they entirely stop flying to a place, and more rights too if schedule changes are very significant in scope, but even then, as Anonba explained, BA would not rebook you, say, from BA to QF. Incidentally, with the QR change, they are bound by the QR rebooking rules. Finally, as you haven't booked a BA flight but a BA holiday, you are dealing with BAH which acts as a travel agent, so again, rules and practice can vary subtly.

What you are entitled to is downgrade refund with is quite generous, but you will likely need to fight for it because that, on the other hand, is something BA is really poor at. They will try to make you accept fare difference but you are entitled to a % of the cost instead based on the part of the total distance which has been downgraded. You can check the main thread on disruption and info on the Mennens formula.

I would add that passengers grossly over-estimate the impact of of the airline they want to be rebooked on being part of the same alliance or not. Essentially, whilst alliance partners do tend to come a little higher than non alliance partners in the pecking order, genuinely, across much of the industry, that is actually a very marginal/limited different. As Anonba mentions, what does make a difference is whether you are trying to move within a JV or not though again in some specific cases (e.g. award tickets with many airlines) even JV partnership will not necessarily be allowable.

Finally, almost universally, schedule changes (as long as they are long enough, often 3+ hours, with some airlines 2+ hours etc) will count more than equipment changes including with forced downgrade. The exception here as US airlines several of which consider an equipment change "as" a schedule change, but that remains the exception rather than the rule and most airlines across the rest of the world will consider that an equipment change opens no (or very limited) rebooking rights.

So I'm not saying that I don't sympathise with your frustration, but in this case, I think that if you switched to another airline and ended up having a similar issue, it would more often than not lead to the same outcomes, and in fact, some airlines - including QR - have pretty atrocious back office and, in my experience at least, are far more infuriating than BA to deal with when things like those you describe go wrong notwithstanding how enjoyable they may be once in the air.