Ripple has no issues, someone transmitting "MemberBerries" money (unconfirmed rumor say he is son of orama bin laten) without licenses will have issues to deal with sooner or later, fact, same as lightning node operators,
The only 100% compliant blockchain is BitCoin (BSV) as it is designed from ground up to comply as in whitepaper.

On scaling front right now

BSV 14000 tps
Komodo 10000 tps
Xem 4000 tps
Eos 3000 tps
Xrp 1500 tps
BTC 6 tps

better get developing before being left behind.
51% attack is somekind of time-warp, it was discussed in 2013. There is a shitton of coins out there where just a modern desktop is needed to do it. In History of crypto i think one coin got attacked (Bottlecaps) and recoverd just to die a natural dead later.
In History of crypto just two coins where successfully hacked, XLM and XRP.