Originally Posted by
Adoxe
It hasn't been like that since Cataclysm it's been like it since Legion when they added scaling to old content, including items.
1-60
58-70
68-80
78-90
88-100
98-110
and 108-120 are the transmog level breakpoints, you unlock the highest level transmog of that point the moment you hit the minimum one. There was a brief moment when this was available pre-scaling by transmogging heirlooms and sending them over to your alts back in Cataclysm and MoP, which was unintentional and fixed, this however is a completely intentional feature that you're gonna have to deal with. Personally, I'm glad that my low level alts, who by the way already looked out of place because of Heirlooms since WOTLK, can look badass even when leveling and show off some cool things that other people around that level might not have.
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Not sure why people are talking about what has and doesn't have a level cap since that has no effect on it whatsoever. Tier 2 sets and the Replica PvP Sets from Vanilla definitely have the level 60 requirement and can be used on a level 1, just like any other items/sets within the level limits I listed above.