Some use Agile as an excuse to take shortcuts, and if you follow that path, then YES I think Agile is bad for design.
However, from my understanding/experience with Agile is that it is about ‘doing just enough to get the job done’ without adding anything fancy or of low value. If a pencil sketch communicates what is needed, no need for hours of fancy modeling. If a document isn’t being used, don’t spend time maintaining it.
First step there is defining what’s needed to get the job done. Every project will be quite different and I feel it quite often comes down to the stakeholders involved.
If used as a means to remove waste activity, as opposed to taking shortcuts, I believe Agile can be a very useful tool to have in your belt.