There is no reasonable scaling for solo content bosses regarding their stats when you can choose a difficulty setting. The stats are always high regardless which difficulty you choose, I think the entry level is way too high even with +16 equipment, it takes a long time to clear and you still get only a low portion of the maximum rewards.
In my opinion, the stats should be taken at highest difficulty and then divided by difficulty level, Tel Harsha at difficulty 1 should only have 1/7 of all the stats (including HP,defense,attack,critical resistance,evasion) that Tel Harsha stage 7 has (same with Moringponia stage 1 having only 1/5 of the stats of stage 5) so the entry level is low and newbies can start farming solo content early with reasonable difficulty levels.
Right now, they start and see all the solo content they cannot do every week and thus lose lots of potential loot.
With reasonable stat scaling that makes solo content a breeze, they can start beating the solo contents at lower difficulties easily, allowing them to stack materials right off the bat when they start, and begin tackling higher difficulties with higher stats when they get there.