I do not have a completely fair comparison. But a migration from Elasticsearch 5 (2016) to the Vespa 7 (2019) we reduced half of our nodes, and cut in half the average response time. Another amazing feature during the migration, is that Vespa allows you to reduce or increase the number of nodes dynamically. And it take full care about the data distribution.
In ES we (used to) had to follow the limits of the pre-configured number of shards/replicas during the Index creation.
It should be marketed better, I feel. Some SEO for "Solr/lucene vs X" queries might help. I have been spending the last 3-4 months studying open source and commercial search systems, but it's only in this thread that I discovered Vespa.
This may be of interest to you: https://sematext.com/opensee/report/project/trend?q=ElasticS...
Would you happen to know how Vespa compares to ES in terms of memory or CPU footprint? Have you done apples to apples comparison by any chance?