Weakness: Never had a great offense as Head Coach
While Dennis Allen has always done a good job as a defensive coach, his offenses have left a lot to be desired whenever he's been the head coach.
With the Raiders, he saw his offensive ranking dip every season. He started out 18th in overall yards then it fell to 23rd and 32nd to start out the 2014 season prior to his early dismissal. They were also struggling to score points, finishing 26th, 24th, and 31st in those same years.
This past season with the Saints, his unit moved the ball better than they did in 2021, finishing 19th in yards. But they were 22nd overall in scoring.
Typically, coaches such as Allen don't seem to take as much heat for a struggling offense since it's not their specialty. Being a former defensive coordinator, it seems as though the first instinct is to consider changing the offensive staff.
However, as the head coach, it all falls on Allen. He might have more of a hand in the defense but he has to be able to help his offense as well.
Plenty of head coaches made it to their current position due to their performance solely as either offensive or defensive coordinators. But the ones that truly find success are able to manage all phases of the game.