Yes, but if you put enough into it, say putting 10 SBD into it, it doesn't matter if you lose 10% or even 20%.
Because it pushes your post up higher into hot/trending section of whatever place you posted it in (your 5 tags). So really, it is a better deal than paying SBD to promote the post through the Steemit function. So your opportunity to get more followers and even more upvotes is a lot better when using a booster(assuming you don't lose 100%).
But yes it does suck to lose money on it I would imagine.
If that makes sense :)
In theory I think you are right. In practice I am constantly filling my niche of education and memory with tons of ranking articles and the amount of new followers has actually sunk DRAMATICALLY since then.