Not being a first author diminishes the contribution of co-authors?
It depends on the subfield of computer science. For example, if the paper is in theoretical computer science, then author order is alphabetical, and the equal work put in by the authors is not negated by the author ordering. If in a discipline where author order is meaningful, then it's standard practice to (say) order the authors alphabetically and add a footnote saying that all authors contributed equally to the work.