> If you know that your password has high entropy (>128 bit)

I don't think that is practical for most users - 12 words (or 10 taken from a 10k list) - or 22 random alphanumeric characters - is hard to remember - and long enough that they are difficult to type correctly. 70 bits might be a more sensible goal - but still long. (6/7 words, 12 characters from a set of 62).

This is the "trust anchor", so something the user needs to remember and type in - from what I've seen - remembering/representing and inputting 128 random bits is tricky.

And with modest stretching and a salt, probably overkill anyway.