Monero is less scalable [than Bitcoin] because you have to store all transaction outputs (key images) instead of just unspent transaction outputs, since Monero does not know which outputs are fully spent (for larger ring sizes). And these must all be stored in fast random access memory for double-spend prevention. That’s an ever-growing pile of data!
While in Bitcoin, you can offload older UXTOs to a slower memory, because the access pattern is “UXTOs die young.” Also, UXTO set grows much slower or even can be stable (“1 UXTO per person”) while transaction volume grows forever.
Bitcoin scales way better than Monero or Zcash (that has the same requirement to store all “nullifiers” to prevent double spending).
2017-12-29 | Full Review