Nice find @NateP! Outside rides without power data but with heart rate data will contribute to AI FTP Detections after the initial calibration. Though as Nate mentions having a power meter is obviously going to be best.
@Mdavidford I suppose you’re right — most people’s goals might not necessarily be to simply ride their bike faster, but being strong enough to ride quickly can help you win a race, complete a bike ride before the cut-off, and beat your friends in a town sign sprint!
@Scase73 I agree with @NateP’s original response — “Some structure will be better than none.” You’ve got less than three months before Ironman Wales. Keeping some consistency around structured training, even using RPE, will help give you an opportunity to perform well at your last “serious” cycling event. 
I wouldn’t worry about a power meter if it’s not a priority. You have access to that data through your smart trainer via TrainerRoad to check your progress whenever you’d like.