Their wording was something like

"We have plans to make sure your relics/etc you've taken to 99 wont go to waste".

They said nothing about buffing them, for all we know owning the 99 R/M/E could just mean they'll give you a quest to unlock their weaponskill or allow you to use them in your offhand. (though the WS thing makes little sense for Mythic). Either way, They said nothing of buffs, simply those weapons "Wouldn't go to waste", which sounds more like an afterthought or "They won't be completely useless, we promise!".

They also specifically said they would not improve them through trial of magians or any other means, which means their only options are a flat out buff too 99 R/M/E or... Prepare to use them in a quest to unlock their Ws's broseph.