Cryptocurrency decentralization definitely suffers when the concentration of hash power or the number of coins is concentrated in a very small number of hands, which, if necessary, can collude with the aim of gain. Moreover, Ethereum will switch to PoS mining in the future and it is not clear how this will affect the network if a third of all coins will be placed on only 376 wallets.

MyEtherWallet is a safe wallet, but I also use Coinomi, I like it, it is convenient and safe. Or Blochain.info but the developers in it introduced the KYC system and I stopped using it although it is also convenient, secure and allows me to store my private keys where I want.

In principle, Ethereum can be stored in any wallet that allows you to store your private keys. I like Paytomat, you can store different coins, tokens Ethereum, EOS, Binance and other projects in it. There is the possibility of staking the token of the Paytomat project for profit. Convenient for making payments and provides private keys.

The price of Zcash fell probably due to the appearance of ASIC for mining Zcash, because many GPU miners switched to mining other coins on a different algorithm and interest in Zcash from their side decreased. All of this has a negative impact on the price and the size of the Zcash community.