While IB can certainly be frustrating to deal with if anything goes wrong, I think they treated me more than fairly as an AA Plat when I lived in Madrid.

I had lounge access in MAD when I was traveling anywhere on IB or BA (which was pretty much wherever I wanted to go) even though I was on discounted Y tickets.

I was even upgraded once to J on a domestic leg (within Spain.)

Once, BA lost my golf clubs on a trip from the UK back to MAD and IB was charged with delivering it. It took 6 days, but everything was intact. And no, they were not sympathetic.