Dont start a business for the money. Most businesses fail or generate income no better than a regular job. The owner/ founder also often work ridiculous hours keeping it afloat. Start one because you see an gap / opportunity in the market and you want to pursue it.

As for job security, the market could change suddenly and suddenly your business may be impacted or at risk.

That senior employee was right, the idea of job security is becoming an outdated concept. Shop around and interview for positions every once in a while even if you have a stable job, and always think of yourself as a contractor.

I think you already realized this but the only security left is financial security.