Language - especially spoken language - can be learnt not word by word, but pre-fab by pre-fab. That speeds up processing and improves fluency.
In statistically based lists, frequently used idioms are definitely covered (a little bit, a lot of, be able to, etc), but such lists include many more useful items (well I think, oh I see, but I mean, etc).
If you want a list of conventional idioms, a dictionary might be better. But some idioms may fall out of use gradually (rain cats and dogs, hen-pecked husband) whille new items become popular - a life circle.
I found the lists extracted using Michael Barlow's Collocate are more "idiom-like" than those from WST. Or even better is IdomPrinciple developed at Birmingham, which is for in-house use.