Question about mirrorless

[Major Nikon]

6. The biggest issue is the use of legacy lenses

If you have thousands of dollars invested in SLR lenses you really like, switching to mirrorless could involve a significant investment.

The advantage to SLR in terms of low light will be with manual focusing in certain circumstances. If you have a split image focusing screen for your SLR you might be able to focus better in low light situations simply because you have an optical rather than a digitized indication of focus. However, even a split image screen suffers from the same handicap as it also works on differences in contrast. I would expect the differences, if any, to be small.

The advantage to mirrorless is a smaller/lighter camera and lenses all other things being equal. If you are just getting started buying higher end equipment this advantage far outweighs any disadvantages.