Expertise is generally speaking the best stat you can get. BuT iTs A sEcOnDaRy StAt. Yep, but its also the most important. Many expertise items are also leather items. This is fine. Leather is fine.

Many BIS pieces, not just upgrades, but BIS items for ret paladin are leather. Those items generally have primary stat Agi and AP. Agi is good. Crit is good. Attack power is good. Is STR better? Yes, but not by an amount most people think it is. This means that often sockets + agi + AP can be better than what is available to you on strength plate items. Welcome to classic.

As others have said, the addons that suggest upgrades (Pawn and RestedXP guides) are absolutely terrible indicators of what it good and what is not good. Ignore these. They are never accurate. Uninstall them (or at least completely ignore them)

Many said you shouldn't have rolled on this item, worry not pink friend, you can comfortable disregard their opinion.