Sluggish can mean all kinds of things to different people so it is not a useful metric term. Network latency, disk drive latency, and startup times are the usual culprits. However other items like background colour and  font look and feel can give people the feeling something is 'sluggish' or 'slower' versus another system because a mouse will 'feel' like its slower than in another due to human brain wiring than actual facts. As such, I would just take it as a figure of speech which would need careful testing to see what was going on before seeing what might be the cause.