The windows are tiny
If you see a prototype, you will note that the cabin windows are bigger; the windows shrank due to a certification requirement. In the course we were informed that, with all four a/c groups working, cabin pressure could be maintained with two windows missing at 60 000'.
cockpit is blocked off with clear Plexiglas, but looked decidedly primitive by todays (or even 1980's) standards
Possibly so, on first glance. In reality it was considerably more sophisticated than its contemporaries (e.g. 747-200), and the systems behind those switches immeasurably more so.
There's not a lot of space for the necessary controls in the front of a pointy aeroplane, and this was done in era when the appearance of the flt deck was inconsequential compared to its efficiency, utility and safety. It's only from the beige cockpit Boeings and onwards that the trend has emerged to for all these swoopy trim panels to be fitted for cosmetic reasons.
As for commercial failure - that may be true for the constructors but I can assure you that there's no way BA would have been flying them if they didn't contribute to the bottom line, let alone invest in the return to service programme.
It always pays to remember the context of operation of this machine when making comparisons with conventional aircraft,as that's what drove much of the design.