This is more a problem with Ethereum rather than with "standard" crypto. For mobiles you have "SPV wallets" that does communicate with many other nodes while v

This is more a problem with Ethereum rather than with "standard" crypto. For mobiles you have "SPV wallets" that does communicate with many other nodes while verifying block headers and that the transactions you're interested in are included in the blocks. So an SPV wallet doesn't contain the whole blockchain, but to cheat it (and make you see invalid transactions), you need to generate a fake block, which is just as expensive as creating a real and valid block. And all that's needed is for you to find a single node you can communicate with