I think people obsess about numbers these days (no offense, not specifically you, I myself might be even more prone to it!).
Short story: A friend of mine (who happens to be my best riding buddy) rides the trainer exclusively from November to February and doesn’t even follow a plan. He just does his endurance/tempo rides and the occasional hard effort. He uses no power meter outdoors and trains only based on HR for endurance/tempo/LTHR and “sustainable all-out” for different interval lengths (read: strava koms 
)
He sits at 4.5w/kg (320watts) FTP and holds almost 90% of that for 2hours with 10hours/week. (Has barely top end though, but is happy with that)
Yes, maybe he is genetically gifted and who knows how good he could be if he followed a structured plan with power.
I find myself making good gains (momentarily at 4w/kg 280watts) with a year round structure but
hold it … hold it … here it comes …
who knows how fit I was if I “just” rode consistently with a raw structure of mainly endurance and the odd effort?
Yes, training without power meters is less effective, but training with power is also eking out the last bit of potential (I would not want to miss my power meter out of curiosity and to track progress though).
I honestly think that having a power meter translates “just” in as much gains as really nailing 8-9h sleep every single night (instead of sleeping 7-8/hours with the occasional 6-7hours) or having a pin point nutrition plan where 18 out of 21 meals/week are exactly calculated (and I’m not talking about “just” being aware of eating how many calories and vegetables, fruit, proteins, carbs at any given time. That would be “just” HR-training)
Bottom line: Yes, training without power is less effective. Is it really that much less effective not to speak of “way less effective”? I doubt that.
I hate to be so negative and I really like the idea of using the possibilities of modern technology to seek improvement, but …
Would a pro rider use something like AT? No of course not, but he also has a top coach, who not only knows everything about training but also monitors the athletes life.
So the question for me personally really comes down to this: A (half cooked) AI or a shitty coach? I pick me