Hello @larine,
and welcome to KNIME Community!
Well I’m not a developer (so someone will hopefully correct me if I say something utterly wrong) but would say it’s because Column Expressions is based on JavaScript and Rule Engine is based on Java while KNIME (which is based on Eclipse) is Java based so every node that uses Java underneath is faster (or at least should be if implementation is proper) than node which does not use it (and of course both do same calculation). Makes sense?
I like Column Expressions very much as it offers possibility to replace many nodes using multiple logical expressions with calculation together with some fancy functions but I suggest to use “Java” nodes like Rule Engine, Math Formula, String Manipulation in case of loops and processing huge amounts of data. Especially for your use case where you only need to use one node to replace your logic from Column Expressions node.
And Column Expressions actually did get significant speedup with KNIME 4.2.1 so if using older version consider updating.
Column Expression Speedup with 4.2.1)
Hope this helps!
Br,
Ivan