Generally Elixir programmers are fully aware of its strengths, and how they outnumber its weaknesses, hence are not insecure about it 
so are happy to be open and frank about where other languages may be ‘stronger’ (whether, as Michał mentions above, because we lack tools or optimisations or whatever else). However I agree that we need to be mindful of how that may come across, especially to newbies …perhaps by highlighting that it is rarely a problem for most apps.
For instance, number crunching is often referred to - but in what context? If image manipulation, then we can just use ImageMagick (or some other library written in something like C) and which is something we commonly do in all sorts of languages (like Ruby, PHP, etc) with wrappers or tools such as Mogrify or Arc. If you need even more performance than ImageMagick, you can use VIPS, which also has an Elixir wrapper.
The other common one is Machine Learning, but now we have Tensorflowex 
With regards to native UIs, we now have Scenic
