It was 53.4% more, not double, so let's get the facts straight
$5800 vs $8900 for the US version.

I paid a few $75 change and cancellation fees last year on the Flex pass. There were other times when it looked like another flight would have slightly better upgrade odds, but not enough to warrant a $75 fee.

There were other times when the flight I wanted was M0, and times where it was down to M3 at T-14, so I couldn't wait until my upgrade window to book.

And there were missed upgrades even as SE on M fare on SFO-YVR and YUL-YYZ (and more missed upgrades as I look back in time through different status levels).

So with the Latitude pass, aside from the 25% COS bonus, I can book all my flights for the year now, and confirm upgrades for 2 eUps each way. I can make any changes and cancellations I want to, at no cost. I can convert from R to J at T-48, and then I have what the airport agents see as a full fare business ticket, allowing me to do whatever I want at the airport. "Missing an upgrade" is no longer something that even remotely worries me when I book with it. And if something comes up last minute, I don't have to hunt for M availability (which is actually a problem more than you'd think when the route I'd be booking is SFO-YTO).

I have a growing number of elderly family members, if you get my drift, and there are less drastic events that might require I see family on very short notice. I haven't had to use the pass for this yet, and I hope I don't, but a full Y fare SFO-YYZ purchased one day in advance is $3356. That's more than the difference between the M pass and the Y pass, and it is not nearly as certain of a seat in business class as the FP. So in this sense, it's almost an insurance policy, that still pays out in other ways regardless of if I need to cash in.

But it really comes down to the value I place on $3100 compared to all those benefits. For me, the benefits win. And without going into specifics, AC sees a Latitude FP purchase as high revenue from one person, which has other benefits.

Last year, I did a fair bit of mileage running on UA in Y. This year, I've done some "jogs" where I take a weekend trip somewhere, and explore a new city, sit by a pool with a drink in my hand, or something else enjoyable. But I am not doing any MRs this year (excluding anything like EYW). The 25% helps me with that