No, that's not the problem.Of course I do. If you have X total excess deaths, but many of them aren't from contracting the virus, then the total excess deaths represents a larger number than the excess deaths caused by the virus. Algebra.
a) you need a reasonable estimate for non-covid excess deaths. You can't just pick a number you feel like.
b) not all covid-19 deaths are necessarily recorded as covid-19 deaths; the official tally may be an underestimate (there's that researcher in Florida who claims the state government has been deliberately under-reporting, although I have no comment on how true that is), but they may show up on excess deaths.
c) excess deaths is inherently of limited reliability due to variability in annual deaths; for instance +/- 10% may die in any one given year compared to the average of the last five years.
d) and finally, that's 300,000 excess deaths estimated by early October. A lot of people have died of covid-19 since then. The 320,000 is an up-to-date figure. Well, as of when I posted it anyway, it's already over 330,000 by now. There's a decent chance it will be over 400,000 by the time Trump departs the White House.