Buying would refer to buying shards from shipments or weekly shipments, in my book.
That's a pretty fair use of the word.
BTW: 2/day is definitely possible on 15 sims because RNG is RNG, but on average you'll get about 3 shards per 10 attempts. If you got less, someone else got lucky and got more.
Since you don't know in advance what your luck will be, guessing 3 shards per 10 attempts (4.5 for 15) will get you a decent time estimate. I always take whatever the average/expected value is and add 20% to the number of days so that I'm not disappointed by bad luck.
Right now I'm at 61/65 on BoKK, so 189 shards needed, with expected 3 shards/day.
189/3 = 63.
63 + 20% = 75/76 days. So my plan is 2.5 months, but any double drop event or if I'm ahead with everyone else's Kyros & don't need crystals for that, I can drop some extra refreshes & accelerate that timetable.
If I was doing 15 attempts every day, I would expect 1.5 times more shards, so 63/1.5 = 42. 42 + 20% = 50 or 51 days.
Again, this is just averages (with a cushion) so it's still possible for your plans to go badly, but overall it helps me to be able to approximate things. This way I know how urgent it is to buy gear, for instance. If my farm toon is going to be done quite quickly, I might accelerate gear buying to make sure that gear doesn't hold me back. Or I might have to farm signal data even faster.
But if the toon is what's holding me back, I can do 1 fewer refreshes on signal data farming and invest that into gear or farming more shards of the toon.
Having reasonable expectations helps you make better plans. 2 shards per 15 attempts might be what you got for a couple characters, but it's not a reasonable expectation in advance: that's pretty bad luck.
