IMHO the blame for that lies with the software, not the hardware. Android is basically the realisation of the original Java OS, but on hardware fast enough that its performance has become "acceptable" - most of the time.

As for the other features; Bluetooth, WiFi, accelerometer (and compass/magnetometer), SD, dual-SIM, and removable battery are pretty much standard on every generic Chinese phone now since they're based on reference designs that have all those components (they cost almost nothing - it would probably take more work to remove them and customise the HW/SW - and it's yet another feature point they can list.)

I'd consider such a "full-featured" phone "flagship", but what the term appears to mean today is just a fast CPU, big screen, and pretty looks, with the other features appearing and disappearing seemingly randomly.