Requiring would be ascensionists of a harder route to climb an easier route in order to rig a top rope may lead to accelerated wear of the holds and gear placements on the easier route. (The effect being exaggerated the more popular and/or prone to sieges the hard route is).
If said easier route is good in its own right, seems a shame to expedite its degradation if another solution (such as a minimal bolt ladder on an unclimbable section) could be implemented.
Obviously all crags have their own subtleties and accepted practices, and change should be sought in the appropriate way for the venue.
I’m not familiar with the crag alluded to here so this is more of a general musing on purism vs “accessibility for preservation” than a proposed solution to this specific example.
Ultimately it’s an ideological debate, traditionalism vs progressivism. The traditionalists want it left alone and the progressives want to install an access ramp. Both sides provide arguments for and against their wishes, with the progressives currently spouting post hoc justifications for their actions. Personally being in the traditionalist camp, I believe it should be left alone and even to go to seed if no one climbs it. IMO the e9 was put up by a progressive as part of an odious business advertising campaign.