Is it worth buying wild sets and then disenchanting?

Should I go though and buy old wild packs and disenchant the legendary you get within the first 10 packs. Is it worth it in terms of just getting dust? It certainly seems worth it considering the 10 packs it takes seems like the minimum, and on average you get it within the first 5

Depends how deep your pockets are.

It’s about the same;
You need to dust 4 Legendaries to craft one.
Lets say you get the worst luck and open each set’s Legendary on the 10th pack, that’s 40 packs.

Worst luck means you’d get a Legendary on your 39th Sunken City pack.

Let’s say you get average luck and you get your Legendary on the 5th pack of each set, that’s 20 packs.

Average luck means 20 Sunken City packs.

Also remember, if you’re opening Sunken City packs, you also get all the commons, rares and epics that are relevant to the current expansion, rather than the ~quarter value of DE’ing irrelevant wild cards.

Conclusion: In my opinion, no, it’s not worth it if you’re not going to run Wild. Just open current expansion packs.

But if You Open 10 packs and find the Legendary, You Also Open 37 common, 10 rare, 2 epic, it is 585 dust more the 400 from the Legendary

True, but instead of opening wild packs and dusting them to craft standard cards, you open standard packs and get standard cards that you don’t have to inefficiently craft.

If you’re new, I recommend buying normal standard packs, that way you can actually use the cardw you get if they’re good and not have to dust them.
However, if you’re using the pity timer trick (after a set number of packs from a set, you get a guranteed legendary) then buy packs from one set until you get a legendary, then move on to another wild set.

IMO just go for standard packs, return value from dusting 1 legendary every 10 packs is just not work