First off, I made the mistake too but, let's get it straight. It isn't MLB's steroid penalties. It's MLB's PED penalties. PEDs are a wide ranging category of seemingly arbitrary drugs. Cortizone shots - OK. HGH - not OK. Caffeine - OK. Ritalin - not OK. etc.
As Parkes said, several players have been sidelined with drinking too much caffeine which certainly fits all the criteria you've pointed out so far. It's harmful, it improves performance, and is marketable to high schoolers (and is actually accessibly to them!). They can see Josh Hamilton's contract and say, hey, Red Bulls helped him get that, lemme down a few before every game.
"This isn't hysterical when you consider the fact his use of juice is what got him the contract." That's a pretty unhealthy oversimplification and makes a lot of assumptions which we simply don't know. The direct effects of steroids on performance aren't well quantifiable (yet?) and, by most accounts, are seriously overblown.
An illegal bat gets 10ish games, spitballs go unpunished, and on and on.
The punishments for PEDs does fall in line with the rest of their suspensions. What makes specific 'PEDs' illegal seems arbitrary and, overall, MLB's policies seem rather poorly thought out.