Lightweight (SPV) wallets will blindly trust the miners
Not completely blindly though. A SPV client will still verify everything there is to a bitcoin block header and also can fetch merkle trees and verify existence of a transaction in a block. They can also connect to multiple full nodes and monitor the situation with the bitcoin network (forks, stale blocks, reorgs,...) and know whether the block it has are still part of the chain or not.
meaning if 51% of miners printed infinite coins or spent the same coin twice then lightweight wallet users would happily accept these fake bitcoins as payment.
This is not a light-wallet specific problem. A 51% attack affects full nodes and SPV clients the same. And invalid transactions ("infinite coins") are not part of the valid chain anyways and both full nodes (by full verification) and SPV clients (by querying multiple nodes and following the longest header chain) will recognize it.
Early adopters are unfairly rewarded
I'd like to point out that I've been hearing this statement from different users ever since 2014 that I got involved with bitcoin and they will repeat it in the future too. Funny thing is that if they bought bitcoin in 2014-2015 instead of nagging they would have bought it at about $400 and now the price is about $40,000 which is 100 times higher.
Funnier thing is that those who are nagging today and not buying bitcoin will complain in the near future when price is $400,000!