Is `<` an unsupported expression in rollupJoin's?

Question

I am trying to use a rollupJoin pre-aggregation as per this example but instead of joining on an ID I am attempting to join using dates, i.e. something like:

joins: {
  Weeks: {
    relationship: 'belongsTo',
    sql: `${Weeks.startAt} < ${Event.closedAt} AND ${Event.closedAt} < ${Weeks.endedAt}`
  }
}

but am receiving the following error:

Error: Error: Internal: SQL error: ParserError("Unsupported expression \'Lt\' in JOIN condition") disabled backtrace

I can't find any explicit documentation of these operators not being supported. Are they not supported or am I getting the syntax wrong?