"You can’t diversify if you can only save a thousand pesos every month, don’t you? Even if you do so with 100% returns, it will only make another thousand pesos monthly."

This is wrong in two ways. First, even with only 1000 pesos, you can buy shares in an Exchange Traded Fund (ETF) that's invested in a market index (in the US that would be e.g. the S&P 500. That's some pretty significant diversification right there.

And if that's not enough, you can split it among three ETFs, once for domestic stocks, one for international stocks, and one for bonds.

Second, don't look at short-term returns. If you invest 1000 pesos this month and get say 6% annual inflation-adjusted return, it'll double in today's dollars about every 12 years (look up the rule of 72).

If you're, say, 25 years old and are investing for retirement in 36 years (age 61), money you invest today will increase 8-fold by then. Of course, money you invest at age 49 will "only" double.