I've spent the last year messing about with sugar in beer and I am starting to reach the same conclusion that I prefer all malt beers.
But it is a personal preference! I suspect others prefer beer stretched out with a bit of sugar. And some of the beers could tempt me away from "all-malt".
I casked my latest brew yesterday. 12% sugar, an attempt at a "Mild" Ron Pattinson dug out from Truman's 1909 records for an "X" ale (
Truman 1909 X). At SG 1.057 not a "Mild" like we know them now-days. It has an FG of 1.017, slightly higher than Ron had gleaned (1.014) but wouldn't fit your description of "thin"; I was manipulating the mash a tad to prevent it having a "dry" finish (the choice of yeast also has to be important in this). Emulated "No.2" Invert Sugar, giving it some colour (dark amber, still way off "brown"), much like the Ragus emulation of "No.2" Invert Sugar (and certainly none of that historically incorrect
caramelised sugar nonsense you see bandied about). Next on uses "No.3" Invert Sugar (19%
); 1937 Whitbread '33 (a "Burton Ale") from Ron's "Strong Vol.2" book' another that will not be "thin".
I've only been playing with "Invert Sugar" emulations. But other sugar additions (even the "caramelised" nonsense) must have their place. Don't let yourself be put off messing with sugar, but I agree with you, "all malt" is best!
(BTW: I don't "invert" my invert sugar emulations 'cos there is absolutely
no point wasting the time and effort).