Coggan was right when he said this:
What I’d like to see is a study that looks at a group that trains 3-6 hours per week on the bike split up into 3 cohorts: Add 3 hours of strength training, Add 3 hours of Z2, Stay at 3-6 hours of cycling, and compare the results. (Actual hours could be flexible, but low - medium ish volume)
Then look at a higher volume group where you can’t just add hours, or adding hours puts you up against what you can recover from:
Look at a group that trains 10-12 hours per week on the bike (or more). One cohort stays the same, another subtracts 3 hours of cycling time and replaces it with strength training, another adds 3 hours on top. Compare.
The fact of the matter is, it’s a trade-off. You can’t just unilaterally add more hours, so there’s an opportunity cost to everything you do. If you want anything like this to be a “fair” comparison, you should compare the added time lifting to added volume on the bike.