That’s right. Blockchain formation is a security measure (with merkle roots and tree), pretty slow.
To achieve fast transactions, masternodes have to focus on CONSENSUS, not on SECURITY.
Security, that’s to say blockchain formation, can be delayed a little bit, for example a few minutes.
A fast consensus can be achieved through off-chain pre-confirmations. For example something closed to Dash Instantsend.
In a network of masternodes, deciding whether a transaction is legitimate or not can be achieved within 10-20 seconds with a reasonable level of confidence.
And it is very scalable : such a network of masternodes can manage hundreds or thousands of transactions per second.
My idea about off-chain pre-confirmations was explained in this post : Increasing scalability thanks to delayed blocks formation