You're not mistaken about clearing the purchase limit, you're mistaken about how much long it takes to load everything on a carrier vs the alternative, delivering it in a properly outfitted long range cargo ship (which takes much less time and effort to get than a carrier).
Assume a small loop, call it 3 stations. I take my carrier nearby. I run the loop: 3 jumps, 3 cruises, 3 docks, 3 launches, then I jump to carrier, cruise, dock. Transfer cargo. Repeat.
Instead, I take a
long range cargo ship. 200 ton capacity, like you mentioned. I run the same loop. I jump to my point of sale 150ly away: 3 jumps. I cruise, I dock, I transfer, I repeat. This process adds 3 jumps. The point of sale is two jumps further away than my carrier, and it takes me one extra jump empty to get back to it. That's 3 extra minutes. How many loops are we going to do? Let's call it ten. In ten loops, I've spent 30 minutes more than the guy with the carrier. But he still has to fly his carrier to the destination, load his cargo on his cargo ship, take it to the station, and offload it still. The more loops we compare, the more loads he still has to transfer from carrier to point of sale. He hasn't really saved any time. What time he did save he actually spent earlier in the game taking waaaaaaay longer to get his carrier than I took outfitting an Anaconda.
Let me see if I got this right...
So for non FC the loop would be:
start: be in buy system 1 and buy goods (abg from now on), jump to buy system 2 abg, jump to buy system 3 abg; travel to sale system, 3 jumps; sell goods; travel to buy system 1, 3 jumps; goto start.
For FC, the loop(s) would be:
Loop 1: start: be in buy system 1 abg, jump to buy system 2 abg, jump to system 3 abg; jump to system 1 and offload to FC; goto start
Do loop 1 until FC is sufficiently stocked or you get bored, set the FC to jump (maybe even while you log off and go to bed or work or whatever, thus being unaffected by any jump delays)
Loop2: Log in arrived at new system; do back and forth trips between FC and sale station, until you get bored or FC is empty; set FC to jump to buy system 1 and log out to do whatever. goto start
You seem to not value the ability to separate the buy and sale into two separate optimized loops, while also potentially using offline time to cover any FC jumps. You're seemingly also ignoring the possibility of using two different ships for the loops alongside your FC for flexibility; a fast runaround with more limited cargo (maybe even with ability to dock on non-large pads if needed) for gathering the goods for the first loop, and then a massive cargo hauler to get everything faster out of the FC at the sale point without needing to worry about jump ranges (or again using a smaller ship if needed because pads, not every system has a station with large pads). You could even park your FC next to the sale stations parent planet if available, reducing the time spent traveling to and from while unloading.
I don't know if it's significantly faster overall, and it might well not be; but it's definitely sidestepping limits on rare purchases that were set for presumably some reason. And hey, if it's not actually faster or really that beneficial to use an FC for rare goods transport, then no real harm in flagging FC'd rares, yeah?
Also, while it might not have anything to do with FC's... I do presume there's more to rares being disabled than people grinding out merits in a cargoconda, since other stuff was considerably buffed close to levels of what I'd seen from rare hauling; while rare merits were not just nerfed but completely disabled.
Has there been anything more than
"disabled while being investigated"? I've missed it if there has.
Oh and someone do correct me if I got something wrong with the FC abilities, I don't have one so am just going on what I've read and seen about them regarding their capabilities (jumping close to planets, carrying multiple ships, multi kiloton cargo space, offline jumping etc). I could be well wrong on things or they might have been changed. The videos I've seen of cargo transfer certainly don't seem as tedious as you imply it to be, so that's changed I guess and other stuff might have changed too over the years. :/
Though having said all that...
I do think there should be a significant advantage for owning an FC, considering the price and upkeep; so I don't really see all of the above as an issue from a personal merit or credit perspective. If I ever get one I'd sure hope it feels """OP""* for that amount of dosh.
Though as others have pointed out, it might be excessive from a system merit perspective; I don't pay enough attention to that level of PP to... well, frankly, to care... but it doesn't sound great for those who do.
*by which I mean more 'sufficiently powered' than actually 'over powered'