Throughout the summer any crash or increase has been mainly across the board with all cryptocurrencies.

While last year there was some sort of inverse relationship between ETH and BTC, this year they are rising and falling together.

I would conclude that cryptocurrencies as a whole are being invested in, not just one or two. Even if big investors were investing in BTC, that would then trigger people to buy ETH with their newly inflated BTC and so on and so on.

Last year's inverse relationship had more to do with the FUD that ETH was going to replace BTC.