Yes and no.
In the European elections, which typically have a low turnout, have proportional representation (which encourages voting for "other" parties) and which have tended to reflect a protest vote, his party polled highest. It remains to be seen whether that support is durable and whether it translates into success in a First Past the Post election. Support for UKIP evaporated as soon as Leave won the referendum, the same could very well happen once Brexit has happened (especially in the case of a no-deal Brexit).
That said, the Brexit Party (and UKIP before it) have had a disproportionate impact on Conservative Party, and as a result UK government, policy for a decade or more. Personally I'd say that's indicative of the weakness of the Conservatives rather than the strength of the Brexit Party - but as a lefty, I would say that.