I totally agree with that. There was a time where I used machines with both Danish and American keyboard layouts on a daily basis. So I learned to pick passwords consisting of only characters that were located in the same place on both keyboards.
And that was a time when only ASCII was supported, so I had to keep that in mind as well.
The best way to make passwords stronger is to make them longer rather than using more different characters.
I am so annoyed by sites that get this wrong. First they reject my 32 character password because it’s too long. So I try truncating my password to 12, 16, or 20 characters (whatever they permit), and then they reject it because I only have alphanumeric characters. Seriously, the password I started with was stronger than such a short password could ever be. So the weakness of the password I am trying is entirely caused by their low limit on password length and not by the set of characters I had chosen to use.
A user should be allowed to use a password consisting of only two distinct characters as long as it’s long enough and doesn’t have any patterns.