I love the outdoor workouts but do get an inconsistent spread of power over the interval. Used to go way above on inclines /into wind and way below on declines… it is getting better the more I do it. As you mention, the struggle is finding the best sections of road (for me - Eastern Suburbs of Sydney ),… traffic lights, cars and other cyclists all impact. I have taken to only choosing those TR rides that I know work outdoors (usually shorter intervals)… I imagine that is not the ideal approach but I take the view it provides more structure and accountability than when I just go for a ride or try my own intervals.