It looks like this was previously discussed here.
If the command-line switch works, you can use it - but it's a workaround, and usually we try to avoid making workarounds built-in, as it ends up getting messy in the long run. Construct already asks for the high-performance GPU (respecting the GPU preference in Project Properties, which defaults to high performance), but at the moment the Chromium browser engine ignores that. In an ideal world Chromium would support that and everything would run on the high-performance GPU by default without having to do anything. This issue looks like the most recent time it's been filed with Google, so I added a comment there - more votes on that issue might help.