Bane of Empires
Thats hardly a perfect failsafe. And also several chapters coordinating efforts has happened many times before, which is essentially what you just preposed.Concerning the "Crusade Doctrine" I think that this would be very beneficial to the Astartes and the Imperium. If I could arrange it lol, I would have each crusade comprimised with 1000 marines each with its own Commander or Chapter Master. The entirity of its leadership would be made up of a council with chapter masters. One would be voted as "chief chapter master" and therefore have a reign for a certain time. That way a legion under a crusade doctrine could never be ruled over by one individual and in that sense not create a tremendous rebellion or turn to renegade or chaos. Thats the best way I think Guilleman would be happy without using the dumb chapter rule.
And whats your reasoning behind your opinion that it was a mistake to dissolve the Legions in favour of Chapters?