Will investing only in small & midcap mutual funds give a good return after 10 years?

No. Investing in only type of asset class could lead to an underperforming portfolio over the long term. Small and mid-caps did well in the last few years but over a longer time horizon the returns have evened out.

A wise strategy is to invest in a about 3 to 4 fund types based on your risk profile. You can balance the portfolio once a year to ensure that the portfolio overall remains stable and provide steady growth.