Will it be possible if you could elaborate on which coins have dissapointed you so far from your investments? Given the track nature of altcoins in the market, if you closely monitor the prices or if you HODL it for long-term, then the results would most likely be the same as the prices of some majority of the altcoins depend on the price of BTC as well.
Personally, if you plan on HODLing long-term, then investing into BTC is the way to go. Similarly, there are people who compare BTCs as to investing into blue-chip stocks as its price may be high but the returns are somehow guaranteed in long-term investment.
The main reason why I prefer BTC over other alts is that price of alts are mostly dependent on BTC price fluctuations. Till date no alts has reached its peak or ATH while BTC is down and out (there may be few exceptions but its the trend). If somebody wanna go for diversify portfolio then he should built portfolio in such a way that 70 to 80% of his investment must be in BTC and rest should go in alts (top 20 alts at CMC).
Whether you invest in BTC or alt, key factor to success is patience aka HODLing. There is no way you can get rich overnight.