The Short Version
The claim that engine displacement is "one of the most important" engine characteristics is well-supported. Multiple credible sources — including Chase.com, The Drive, and automotive training references — describe displacement as "key," "crucial," and "fundamental" to engine performance and classification. The claim uses modest, non-exclusive language ("one of"), which is consistent with the fact that other parameters (compression ratio, turbocharging, valve timing) also matter significantly. No credible source disputes displacement's top-tier status among engine characteristics.