You can definitely detect a portion of halting machines this way, but it's probably a relatively small portion because the Busy Beaver numbers grow inconceivabl

You can definitely detect a portion of halting machines this way, but it's probably a relatively small portion because the Busy Beaver numbers grow inconceivably quickly: the longest-running machines that halt can go practically forever, you'd need more time than the universe has negentropy left to detect them.