I would be incredibly surprised if that was true. I know a great many business travellers, and some leisure/personal travellers, who will book tickets at late notice like this because they have no other choice, and I can assure you that few will book business premier tickets (245 pounds each way). I work in an international company with a *lot* of business travellers, and not a single person in the company is permitted to travel in business premier. The point about being fully flexible and refundable is simply not logical - if you're booking at the last minute, you're much *less* likely to need to cancel or change your plans, and anyway companies rarely pay extra for flexible/refundable tickets these days, as few of them actually ever get refunded/changed. It's cheaper overall to buy the lowest cost tickets, and simply buy a new ticket in the (relatively unusual) event that plans change.
But they are allowed to travel in standard premier? So you're saying that a £195 non-flexible (miss the train and you need to pay another £214, bringing the total fare up to £409 single), 30 minute minimum check in, no lounge access and no meaningful catering ticket is considered to compare favourably with a £245 fully-flexible, 10 minute minimum check in, full lounge access and comprehensive catering ticket? Each to their own, but with the possibility of a meeting over-running, delays with transport to Gard du Nord and other possible exigencies, I would not want to work for a company that considers the former to be the better option.
Choosing two other dates at random (3/3 out, 13/3 back) gives a selection of outbound trains meeting the "standard premier <75% more than standard" test, along with almost all trains back. For several of the return trains (actually those with the best times for weekend leisure travellers), the difference is only ten pounds.
You've chosen a Sunday as the return date, and interestingly, it appears that where a Sunday is selected as the
return portion of a journey to Paris, the standard premier fares are around £20 cheaper in both directions - a minimum of £79.50 compared to the usual minimum of £97.50. This is slightly bizarre as the £79.50 fares are not available if
both the outward and return portions of a journey are made on a Sunday.
For a more typical journey - out and back on a random Wednesday in March - the fares are mostly £29 standard / £97.50 standard premier, and there are a few trains at £29 standard / £199.50 standard premier.