[Retric]

Right ballpark but missing a few important caveats. Rocket engines generally throttle down to maintain a constant acceleration, otherwise you need to add more structural support to the following stages which costs weight.

Also, calculating power output like that is misleading. A solar powered ion engine on a probe has constant solar power and constant acceleration but would have increasing calculated power output over time as it keeps accelerating. What’s going on is rather than the engine being more powerful the propellant starts with more kinetic energy.