But that all assumes a poly relationship that centers on the Dom and doesn't include interactions between the submissives.
It also assumes that all the submissives are "equal" partners in the sharing of his time. He may well have one or two primaries and the rest have others as their own primaries, getting together with this dominant once a month or only on business trips....

There are many other types of poly relationships too, not "centered" on the one dominant. Some could involve two or more submissives who are devoted to each other and the dominant is secondary to them only joining them occassionally. But of course, he would "count" them as his own, and maybe correctly, but not getting a lot of their time.

And there are family arrangements where three (or more) actually spend "all" (or most of) their time together. That would change the time dynamics too.

I'm not condoning "ten" submissives by any means, I too think that's more wannasay than realistic, but without knowing the exact nature and construct of the household, it's hard to say yea or nay.

But when all is said and done, trust your own instincts as to whether a particular arrangement is going to suit you. No matter how attractive the dominant is (including mental and emotional attractions,) there are others out there perhaps equally attractive and more suited to your needs. You just haven't met them yet.