def logEvent[A: JsonFormat: TypeTag](level: Level.Value, event: => A): Unit = {
    val v: A = event
    val tag = StringTypeTag[A]
    LogExchange.getOrElseUpdateJsonCodec(tag.key, implicitly[JsonFormat[A]])
    // println("logEvent " + tag.key)
    val entry: ObjectEvent[A] = ObjectEvent(level, v, channelName, execId, tag.key)
    xlogger.log(
      ConsoleAppender.toXLevel(level),
      new ObjectMessage(entry)
    )
  }

I don't quite know whether to believe what I'm seeing here:

but it suggests far too much time is spent logging (only 12k samples were spent in scalac and zinc)

ManagedLogger.success could be tunneled through to a version of logEvent that accepted a pre-stringified tag, rather than a TypeTag.

I'd really suggest use of ClassTag instead of TypeTag as the key here, although there might be a good reason that you want the generic types.