True, and of course DC is closer to PR in vocal style than, say, to Ian Gillan. Rodgers was in the midst of building Bad Company when he was approached and perhaps also a little doubtful whether he should be following someone like Ian Gillan with all the high screams. Maybe DP's organ-heavy sound was not to his liking either - he certainly vetoed Jon Lord joining Bad Co after the Purple split (the other three Bad Co members wanted Jon to join them).
I had only read about these demos until now, knew the titles etc. Listening to them now, I'm baffled at how much a clean break DP wanted from the Ian Gillan vocal sound that had made them famous in the four years before. DC on those tapes is closer to David Clayton-Thomas of Blood, Sweat & Tears than to the soprano and falsetto singers of the Ian Gillan-, David Byron-, Ozzy Osbourne- and Robert Plant-school. It was a brave and open-minded move.
Jess Roden and John Lawton were at one point also considered as potential successors for Ian Gillan. And of course Glenn Hughes, who had been the lead singer of Trapeze, was already there, but Purple never envisaged him to be the sole lead vocalist, they wanted to beef up the vocals and enable harmony singing live after Ian Gillan had always sung alone live with Mk II (he harmonized with himself on the studio output though as he had sung in a group with prominent harmony vocals - Episode Six - before joining Deep Purple).