It might be very good. But can such a system compete with one that does use search history as context?
DDG gives more predictable results. It reminds me of why I started using Google over other search engines decades ago.
Imho using the search history as context can also lead to undesirable results, so can funneling people to overly popular results which still can be wrong, had both happen more than enough with Google.
It's a trade-off between spending time arguing with Google if I really meant to search for that word, regardless of " usage, and having to look at more results in DDG until I find the one that I was looking for.
However, I do get your point. Without that extra context, the search results can only ever only be so good.