When an engine rotating assembley is balanced its balanced as a whole right?

So surely if you lighten a flywheel that fucks the engine balance quite majorly dont it?

I mean, if you ran without, or with a different, crank balancer on the other end, thatd fuck the balance in an engine killing way quite nicely, wont it?

What about the ancillary belts running off that end? doesnt things straining on one end of the crank fuck the balance too?