To give you an idea of the amount of work... and because it's germane to the discussion, I thought I'd include the testing I did on mission scaling - though this doesn't include the subjective experience reports, nor the speed of completion etc. There's 400 data-points in this piece alone - and it's not even completed yet.
Summary:
At levels below 220, most players are getting missions with mobs at or below their own level. The missions seem to be spread across something like a normal distribution below 220 too, so that they rarely get mobs their own level and more usually get them a couple of levels below themselves. Also they'll rarely get mobs 5 levels below themselves. The 219 numbers are odd, in that they run to a max of 217, which is 2 levels below their own level (making the missions very easy imho).
At 220 though, there is a sudden jump to mobs being 8 to 12 levels above their level. Given that at 219, the max is 217... the jump is even greater when you ding 220. Also the distribution at level 220 seems to be equal across the board, which means that more players will tend to see the higher levels of missions rather than seeing those in the middle of the spread. When you're only doing one mission a day, some players may only have seen missions toward the top level values.
At least in part, this undoubtedly accounts for the differences that people are seeing. In particular, professions that have toolsets which are more sensitive to higher level mobs - whether by virtue of including level in their defence checks (like some crowd control) or by virtue of being sensitive to higher levels of mob stats (like my mez pets, interrupts on technicians, debuff counters etc etc).
Details
At level 207 I see a spread of mission level (i.e. the level of the mobs in the missions), based on 50 samples for each type, that looks like this:
Terminate Cocoons
203: 12%
204: 50%
205: 8%
206: 20%
207: 10%
Place the Bomb
203: 10%
204: 24%
205: 20%
206: 42%
207: 6%
Salvage
203: 12%
204: 24%
205: 28%
206: 28%
207: 8%
Totals
203: 12%
204: 28.66%
205: 13.33%
206: 25.33%
207: 6.66%
Using the 220 MP, I did the same test, with 50 samples per mission type and got the following:
Terminate Cocoons
228: 20%
229: 20%
230: 20%
231: 28%
232: 12%
Place the Bomb
228: 18%
229: 20%
230: 22%
231: 20%
232: 20%
Salvage:
228: 24%
229: 18%
230: 26%
231: 20%
232: 18%
Totals so Far
228: 20.66%
229: 19.33%
230: 22.66%
231: 22.66%
232: 16.66%
Numbers with 219 MP pulling Daily Missions:
Place the Bomb
213: 14%
214: 24%
215: 22%
216: 24%
217: 16%
Terminate Cocoons
213: 14%
214: 16%
215: 28%
216: 26%
217: 16%
Totals so far
213: 14%
214: 20%
215: 25%
216: 25%
217: 16%