i think Savage means the reverse of your equating
currently conversion = can’t use certain items without potential loss or conflicting, ie have to “think” about using said items/if using the items in setup causes more loss than gain.
If you can disable conversion, you no longer have to do that “think”, savage refers to, about using any items and can use any conversion item you please just for its stats, as there will never be a potential downside/conflict consideration
*speculating ofc
If one of Z’s recent comments is anything to go by tho, it seems like FoA might lean away from “direct” conversion conflict design tho, ie an aether item with % aethher dmg, but converts aether dmg → lightning 
[quote=“Zantai, post:71, topic:144795”]
Morgoneth set’s damage conversions were a remainder of an old approach to item design which has since shifted, especially with FoA sets, where dual-damage sets feature less conversion modifiers while supporting items help fill in the gaps.The set should be viable both in Cold builds and Vitality builds
[/quote]
how widespread that will be/if applicable outside sets we’ll have to wait and see
And it probably wont entirely satisfy what you want, since there might still be a difference vs turning conversion entirely off ofc
(like using a nightblade/Garg belt with vit->cold conversion despite the belt not directly featuring cold dmg still means wont be used for vit builds)