Riding that low of volume, I would imagine your results won’t be too robust (ie ftp estimate will bounce much more than a high volume schedule).
If you enjoy the workouts then keep doing them, but I wouldn’t expect a continual rise in aerobic fitness on 3-5hpw given that you shared you’ve been riding for 2 years. Your body would need much more stimulus for large and noticeable aerobic fitness gains.
At 3.5hpw or even 5, I’d say the riding is just for fun and general fitness. Don’t read into the numbers too much. You’re not doing anything wrong!