Statements do not need to be 100% and "may God strike us down". The buyer is entitled to simply expect and require that good are "as described". If FD said it includes an offline mode, and it doesn't, then it isn't as desribed, in exactly the same way as if they'd sold a camera stating it had an integrated flashgun, then decided at the last moment to leave out the flashgun.
Nor tp phrases about people "bleating" or "whining" help, so kindly stop doing it.
Where I agree with you is that it ALL depends on exactly what FD said about offline mode. It depends, in other words, on HOW they described the product.
Also, whether a refund is full or partial is NOT absolutely at the retailer's discretion. Once delivered, goods can, in legal terms, be accepted or rejected .... and this ISN'T about phydical acceptance but legal acceptance. There are a variety of ways "acceptance" can occur, including doing anything not consistent with having not rejected them (like physically altering, or selling them) OR, and this is the catch-all, not rejecting them in a reasonable time. But .... buyers do have that period, pre-acceptance, to ensure goods comply with the stipulations of the contract, and that emphatically includes the implied conditions embedded in EVERY B2C contract, by the Sale of Goods Act, including the stipulation that goods be "as described".
The SoGA is more complex than most people realise, and there are B2B sections relating to bulk orders, sale by sample, etc where other conditions apply, but in basic consumer contracts, it is also not an option for the retailer to say they supplied 70% of the order, so here's a refund for the 30% of features they did not put in. In is certainly not down to themvto attribute what features consist of what percentage. In my case, for instance, online play consists of 0% of my reason for buying, or intended game play, and offline play for 109% of it. Without an offline mode, I don't want the game if they gave it to me free, because the machine I use for gaming doesn't have a net connection.
What retailers can do, is AFTER a product has bern accepted, is to offer a repair, replacement or, yes, partial refund to account for usage already had. If TV might be expected to last 5 years (60 months) but dies after 13.5 months, they could justify a 13.5/60ths deduction for use.
But that usn't the same as delivering a car sold as having air-con then deducting some random percentage as the part that is air-con. If the car was desribed as having air-con, and doesn't have it, that is grounds for rejecting the WHOLE car, because it isn't "as described".
And the retailer has NO discretion at all in the size of the refund for unaccepted goods being rejected because they breach the Sale of Goods Act. Paetial refunds simply are not an option.
So, thix all comes down to exactly what FD said about their product, what their "description" was, and when and how fast, and under what circumstances, the goods were 'rejected'.
Oh, and under none of this at all does the retailer have "absolute" discretion. That rests with the Courts.