In the last ten years (counting Eurovision style
), Lordi, Lena and Loreen (an L seems to help) have had reasonable commercial success after winning. Norway and Denmark won with typical Eurovision songs that don't work that well outside the contest and therefore their commercial success was moderate. Azerbaijan and Austria won with typical Eurovision ballads that also don't work that well outside the contest and Conchita didn't win because of the song alone anyway. The Common Linnets enjoyed commercial success in 2014, though. (probably because of the L)
The winning songs from Serbia and Russia have no mainstream appeal at all. A ballad sung in Serbian and a cheesefest with a heavy Russian accent couldn't possibly have been a commercial success in Europe but that was before the juries were introduced anyway.
After the introduction of the juries, only Azerbaijan won with a total commercial flop and that song won with a rather small margin in a year in which the 12 points were spread all over Europe. (They should have called themselves "L & Nikki".)
I think this year Australia, Slovenia and possibly Estonia and Sweden could be commercially successful, if they win.
So it's possible to have commercially successful winners and it's certainly reasonable to strive for it. More winners like Lordi, Lena and Loreen in recent years would have been beneficial for the contest outside the Eurovision bubble and their songs don't sound alike at all.