Thinking about this, I agree with @Pusspot on spending more time in Tokyo.
Actually, if a friend asked me the same question about a Japan itinerary, this is what I would tell them. I am biased though!
I’d say skip Hiroshima and focus on Tokyo. If you like Japan and decide to come again, go to Hiroshima then. And perhaps only spend a few nights in Kyoto or Osaka.
Tokyo and the surrounding area offer as much as Kansai (Kyoto and Osaka) with less of the hassle. Basically, Tokyo itself has everything you need. Lots of history and lots of modern. And from Tokyo you can visit Kamakura (temples and shrines), Nikko (mountains, temples and shrines), Enoshima (the sea and shrines), Mt. Takao (mountains and hiking), Matsumoto (best castle in Japan). Even Hakone is a (long) day trip from Tokyo.
Kyoto is great but it’s also extremely crowded nowadays. Buses are the most convenient way to get around but they get packed and the traffic can be awful. Domestic tourists are avoiding Kyoto because of the overcrowding. I much prefer Nara just to the south of Kyoto. Wonderful temples and everything is within walking distance. It’s still very crowded though.
Osaka is fun. There’s nothing really special to see there, but it has a real energy especially after dark.
I would never say don’t bother with Kansai (Kyoto and Osaka), but I would say spend more time in Kanto (Tokyo and surrounding area).