That is a fair assessment of monotone, both in terms of influence and performance, although recent releases have gotten better now that there are a few select large projects that use it (Pidgin, primarily).

Monotone uses a sqlite relational database for the code repository, with built-in synchronization/replication. It uses a PGP-like PKI and digital signature system for its trust rules (allowing for a trust-less store-and-forward architecture that still none of the other DCVS systems support). It redundantly stores both revision history and content diff views (two equivalent ways of serializing DCVS trees), and automatically keeps the two synchronized. It is extremely smart about merging and branch handling (the monotone-dev list is wonderful place to find analysis of edge-case merge behvior). And it did all of this back in early 2003.

Monotone was ahead of its time. It's only “problem” was that its core developers chose to focus on correctness and user interface over optimization, delaying work on performance and scalability until such work would actually be needed... which was much sooner than they expected. Linux was orders of magnitude larger than anything that had been done with monotone at the time. This may be an urban legend, but I've heard it said that ‘git’, the ‘stupid version control system’ was named such in part because it was a grotesque simplification of monotone's sophisticated framework, which Linus Torvalds did hold in high regard.

Monotone is the Lisp of distributed version control... venerable and unsurpassed by anything that followed, but utterly irrelevant today.