I'm interested to hear what you mean by this, I am the excel opposite, I try to make the indoor and outdoor rides as close to the same as I can, (obviously road) not disagreeing with you, I just want to understand what you mean.
My indoor rides and outdoor rides have always been so beyond incomparable, I have scrapped trying to pretend they are both apples a long time ago. Even in my heyday, when my FTP was in that 340-350 realm, holding 200w inside was a total hellish chore. So before this year, riding inside was a non-power based way to bridge myself from one outdoor session to the next.
Ok, so enter the Kickr and Zwift. And 3 fans. Things have changed, but they are not totally the same.
Riding steady-state inside is still hard. I have found that the best way for me to get the highest power numbers is to race. This, by far, will produce my highest 1, 2, 5, and 20 minute power numbers. Compared to outside, they're still lower. But not as much. So for me, oddly, when I am doing shorter, harder stuff, I absolutely scrap the power and go by what the race dictates. The Zwift races are brutal, unrelenting, but free and I don't have to pay BikeReg to do them. They are literally throwaway. My power is a record of what I did, after the fact.
If I am working specificity, I go outside. I simply cannot hold 400w inside for any length of time more than maybe 10 seconds. Outside, it still not easy but I can hold it much longer. I won't get into the "why" of that. it is what it is, it's not a new phenomenon, and I wouldn't be the first person to try and explain it.
Inside, if I am working my power, it's going to be a lower power effort. As I will generally do work like that with minimal elevation (or maybe an Alpe climb) the pedaling is constant. There are literally zero rests. This is a different workout. I can go out, smash out 280w for an hour, then come home and have Strava add 0s and tell me it's really 240w. Still solid but the amount of zero time is significant. So another big difference - it's hard to go outside and pedal 100% of the time. Inside, it's easy.
The rides, and the workouts are just different. So I train different things with different power aims. You can train that CP5 inside, but if you are able to do 400w outside and 320w inside, you're really just producing 320w inside, and not getting the same training effect. So you should switch it up and train the element that works best for the venue you're working in.
Hope that makes some sense.