We urgently need a solution here as well.

Atlassian this is a BUG not a new Feature!!!!
 
If you say that ∑Time spent is only available for standard issues, than why do I get correct results on Epic level except for the subtasks?
It does add up all the time spent correctly from its childs.
 
When issues of the type story have subtasks with logged time and you check the box on story level to include the hours of the subtasks, why are they then not included in the summed total on Epic level.  The checkbox clearly states "include" 
 
Technically I do think that solving this issue is of very low impact.  as the data is already logged somewhere as it shows on the screen under the story. Just a matter of taking the correct value for calculating the Total time spent. 
 
For detailed description and examples see PCS-305281.
 
Again, I hope that Atlassian is taking its responsibility and acknowledge that sometime things go wrong, and makes the effort to correct it.
 
We are paying an awful fee for Jira premium and I cannot accept as answer to this problem that as work around I have to buy some third party add-ons.

It is now more than a month without any news on how Atlassian is going to solve this bug, what they keep incorrectly reporting as a product improvement. Is anyone ever looking into this issue?

Oeps, again an issue that has to solve a bug and which is there already for almost 4 years without resolution.
Current situation is that Time Spent and aggregated Time Spent give exactly the same result, as Aggregated time spent completely opposite of what it says it does, does not aggregate anything at all.