I can easily replace with the 28-70 the missing 70-105 range with my feet
With respect Dirk

I think the replacing with my feet myth is one of the silliest sayings in photography.
You can't walk off cliffs, into the sea, into traffic or last year when I was photograhing Joe Biden I couldn't jump the barrier, get past the police and then have his secret service and SWAT team on top of me and I'd more probably not be writing this if I tried getting closer

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For portraits 70mm is too much 'camera in the face' for almost anybody but professional models, 105mm gets you further back and less anxiety for people. For street photography the longer reach makes you a bit more less obvious allowing more opportunities, that is unless you are Dougie Wallace but I and anyone here won't be the madman he is. BTW look him up as he is brilliant at that but a maniac. There was a documentary about him and worth watching, he really is a street/city people photographer but no way could I do that.
In the days of OVF with film and DSLR f2.8 or faster was required for the view and for the AF to work, much less so with mirrorless. There is still speed, light gathering and subject isolation requirements or preferences for those who want it.
Since moving to FF DSLR recently I find f4 as much as I would want for isolation, I'm no fan of obliterated creamy no info backgrounds and bokeh. I choose my background carefully where possible as it as vital to the photograph and the bokeh from the Lumix 24-105 paints it beautifully and the same with the 70-300. I always want to give a sense of where it is and the need for f2.8 or faster is usually never warranted. Saying this 105mm f4 will do this anyway depending on proximity and stopping down is required.
I haven't done any astro yet with S5ii but try and get your brain around this... 24mm f4 captures more light than my Samyang 14mm f2.8. Hint google 'astro open aperture'. I did loads of astro, astro landscapes, moonscapes and Milky Way with my Pentax APS-C and now have at least a stop extra ISO available, 6400 should be good and just 3mm less focal length with 24-105 compared to 21mm equivalent Samyang 14mm on APS-C.
Sorry for this long blurb. I might get 1/2 decent astro landscapes wikd camping in the west coast of Ireland in August even if total darkness doesn't arrive until 23rd August, besides Scotland you can get nearly the darkest skies without light pollution in Western Europe, Bortle scale 2 or so.