One thing that is still an unknown is what will happen when new bitcoins can not be minted by miners. Nobody knows for sure what will happen then. So in my opinion bitcoin is much of an alt as anything else, in the sense that we can not possibly know if bitcoins are the greatest "pump n dump" of them all so to speak.
That's expected by 2021 if not sooner. 6.25 BTC per block + transaction fees may not be enough reward for miners to maintain the network. No motivation to increase hashpower either, it might even decrease. The cost of a 51% attack over a short period of time could be affordable. A single attack won't destroy the network for sure, but repeated attacks may do. Anyway, they would have a very serious effect on the currency exchange rates and reputation. As for people behind those attacks, they could make good profits.