You are conflating several concepts in the space of a paragraph.
Can patents protect smaller companies? Maybe, if you have the resources to defend yourself in court. If you are seeking investment, you can file for brain-dead patents as a way to prop up your valuation and quiet investor fears. Sadly, this seems to be the main motivation these days among startups.
'Open source' entails a public release of source code and associated artifacts under a copyright grant with certain freedoms. Traditionally, patent grants have not been a part of these licenses, probably because the pervasiveness of software patents is a relatively new phenomenon. It is only with version 3 of the GPL that it gained explicit patent grant and retaliation clauses, and most other open source licenses still don't have such clauses. But the bigger question is what 'open source' even means in the context of Tesla. It is not like they're going to release detailed plans and blueprints from production facilities and upwards that would allow competitors to make perfect replicas of Tesla cars.
'Proprietary' usually refers to trade secrets. If you file something as a patent, which is a form of public disclosure, it is no longer a trade secret.
Most of my peers are strongly against software patents. They don't consider it a moral obligation to open source your company's code or release proprietary information that represents a competitive advantage. In this moral framework, patenting is considered an anti-social act, and releasing source code and proprietary information are considered altruistic acts, ceteris paribus. Note that this doesn't mean that _not_ releasing source code is an anti-social act.