I watched Arrow until season 3. Then dropped it.
I watch The flash.
I don't like Super girl.
I never tried black lightning.
I find Legends of tomorrow hilariously bad (got so much better S2+).
I still watch all the combinations. You don't really need to watch the shows to get them. You miss a little background, and some minor humor moments but that is it.
I'd say I still get 80 to 90% of the crossovers. Several of them have done "self-contained" content. Like Arrow last time was just really about Arrow so I skipped it.
- Deadliest mass shooting by an individual in US history (10/01/2017)
- Deadliest high school shooting in US history (02/14/2018)
- Deadliest massacre of Jews in US history (10/27/2018)
- Political assassination attempt of TWO former presidents(and 10+ other people) (10/23/2018 - and beyond)