Please re-read my post. I prefaced it with: Once you've earned the companion voucher. Once that has happened you can downgrade for a pro-rata refund and still keep the voucher.
So for example you could take out the card, pay £150 card fee, spend £10k in 6 months earning the companion voucher, then either downgrade for a £75 refund or keep it to earn 0.5 avios/£ for the remaining 6 months spend. Thus it would be better to downgrade if your average spend is under £82/day (valuing avios @ 1p).
I did read your post but my point was that the BAPP amex doesn't require and £82 per day spend to break even.
I get what you are saying that once you get the companion voucher you can downgrade for a refund but putting the value of the card as a cost for avios is wrong, the attraction of the card is the companion voucher not the bonus avios. The £150 fee based on a £10k spend gets you a companion voucher and a bonus 5k avios, that is what you need to base the worth on not what you get the net cost of avios points down to.