It looks like you guys have very similar plans!
Use external amp to power at least the front 3 speakers (or all five speakers in the 5.1.4) and let the AVR power the surrounds and/or ceiling speakers.
Definitely all valid options. There’s more than one way to eat a Reese’s Pieces.
It all comes down to personal ideas and “identities”.
I think for most situations, with the exception of multi-channel Stereo DSP Mode, Atmos and DTSX will be just fine with the AVR’s internal amps, especially the higher-end AVR like RX-A2000 and A3000 series.
But everyone thinks differently.
Do your speakers really need an external amp?
Will using an external amp prolong the life of your AVR?