You taking my bit of humor seriously is even better. Your entertaining rant (I likened it to Belushi's classic one, after all) raised an interesting question, though I don't know an easy way to ask b-r.com's Stathead tool to answer it.
/ edit - but by using that tool and sifting around a bit, I found that a slow start isn't as limiting as I thought. Steve Finley, for instance, finished with 304 homers, which by itself I find astounding - and through his age-26 season he had a mighty total of 13. Jeremy Burnitz slugged 315 in his career and through age 26 had only 16. Stormin' Norm Cash, 377 and 22 respectively. Andres Galaraga, 399 and 25. Edgar Martinez, who I should have thought of without searching, 309 and 2 (!!!!). Raul Martinez, 305 and 3, only slightly less of a slow start than Edgar.
And, probably the champ I am looking for, "our own" Nelson Cruz: 464 HR and 16 at age-26. Either a more systematic way of searching, or a flash of further insight, could confirm or deny there is someone else.
So maybe 500 isn't out of the question for Wallner. Who knows, if he plays deep into his 50s, he could reach that 800 mark after all! 😀