No, it isn't "just as safe", by any stretch of the imagination. "Safety", in the context of investing, refers to the distribution of possible outcomes around the expected return of an investment. In most instances, diversification will reduce the standard deviation of the expected return of a portfolio, without sacrificing the expected return. In other words, a diversified portfolio is safer, all else equal. This has been known for at least 70 years. You're not providing any counterpoints to established investment theory. You're simply making false claims that contradict both the theory and the empirical evidence.

But there is zero reason to believe that any of those companies will continue giving the same returns. It's entirely feasible that they will plateau, or even begin to fall, whereas the rest of the market will continue to climb. There are plenty of historical examples of "solid" investments that evaporated over time, so it's not like this is unprecedented.