Assume that the price will reach equilibrium when 80-90% of coins mined each day are sold within 48hrs, for the price to rise it needs more investors willing to buy those coins.
I agree with you. The important distinction is not really between botnets and anything else, it is between professional, commercial-scale miners, using whatever equipment they are using (including botnets) and everyone else (mostly small scale hobby miners or people who enable mining in the wallet because they are already running the wallet so they might as well).
All professional, commercial-scale miners will sell most of what they mine, and they will generally mine the most profitable coin or coins (at least, 100% of the truly professional ones will).
Even then, what matters is not so much whether the miners sell, it is the balance between buyers and sellers. If there are enough investors who would rather buy from professional miners than mine (often because it isn't their expertise or interest), the price will still go up. There is nothing wrong with specialization and therefore trade; it is part of any modern successful economy.