If you're seeing a quest that was not added until TBC/Wrath, report it on the
https://www.warmane.com/bugtracker. Some things, like boats going to Stormwind instead of the Wetlands, are being kept as a QOL improvement. Most things, however, are being disabled/removed if they weren't available until later expacs (For example: Hunters could tame Serpent-Family pets until it was reported a day or two ago, and it was removed as this was a Pet Family not added until TBC.)
If the "Wrath content" you are noticing is the animation, texture, or particle effects from a spell...that's just visual because we're using an unmodified Wrath client. If you get the HD client, you'll visually see the effects from later expacs (for example: Shields like Power Word: Shield and Ice Barrier look different), but their mechanics are (or should match) Vanilla mechanics. I'm sure, if you really wanted to, you could modified your client like the HD client does, only you could backport the textures and effects to older versions from 1.12 client.