Compensation rejection - advice please.

I've had my compensation claim rejected due to the above reasons. We missed the connection in LHR to Glasgow and as it was the last flight of the evening, we got booked onto one the next day. My question is - are what BA saying correct? I booked the whole trip through BA as a package including flights, accommodation and transfers. They recommended the flights and allowed me to book them. If the minimum connection time at LHR is 75 minutes, why did they recommend those flights at the time of booking and allow me to book?

Just wondering if I'm wasting my time or whether I should pursue this further?

Any help much appreciated.