I'm here, where are you?

That said, Hellas is certainly interesting. A few fragments of information.

1) The floor *has* rebounded. The original hole was probably much deeper (A shard of memory says 1/30th of the diameter. Since diameter is 1800+ km, that implies originally a 60 km deep hole, at a time when the planetary lithosphere was only 10 km thick - !! )

2) There is ample evidence for (some) sediment and lava infill of the basin. Question - how much is "some"?

3) At present day, Hellas seems to be an area of nett aeolian erosion. 1 km or more of material seems to have been stripped off the floor of the basin and blown away.

4) The gullies etc are minor features compared to the original formation of the gullies, just as the outburst flood channels and the fretted terrain are minor features compared to the northern plains lowlands "hole" - but remember that the Grand Canyon is a mere scratch compared to these features.