I'm ilvl 278 and I still do not have Hero of the Dawn, so assuming that a solo-player has earned this from the described set of limited options is rather bold.
this is quite misleading. if you want to do high level delves, unless you're on a high sustain class or a tank you're not soloing it...
For hero of the dawn achiev you just need everything upgraded to max using hero crests, assuming you have every hero slot from m+/raid, which for an only char is not that hard to get. And for the high level delves, i did all my L11 delves starting with 220 ilvl on every single alt.
If by hard you mean it's possible to die if you're not careful as a dps in t11 delves, I agree, especially when some accidental big pull happens, but not to the extent that they're not doable.And people here have valeera maxed (60), but it's doable even with her at 30.
why even play an MMO just to play solo?