Let's say; Coin A has a positive correlation of 0.89 against BTC price & Coin B has a negative correlation of 0.89 against BTC price.
Are we safe to say investing on both these coins are minimizing the risk; provided that I will have a good research on both these projects to ensure that these are not shitcoins? Ignore the fact that all coins without BTC is a shit (Note for bitcoin enthusiasts).
It does minimizes your risk but this is not as important as things like proper trade sizing or not deviating from your strategy coz of emotions. Correlation is huge anyways in crypto so if you stick to some simple rules like ETH tokens is just ETH on leverage etc. then you should be fine and not over investing in same concepts. Also important thing is not betting against yourself ! You might go ETH long and EOS short while they are aiming for the same market, e.g. steel industry in real life. Spreading between 2 companies in the same sector is actually quite good way of diversification.