It can affect your focus. Try being around people who don’t get their daily soda or coffee fixes. Heck nutrasweet is addictive, no diet cokey makes them go bonkers.
Yes it has an effect. Everything had an effect. Drinking water affects your focus (usually positively, but not if you cant find a bathroom)
But to say the effect of sugar (unless you are a severe diabetic) or caffeine is somehow equivalent to THC is disingenuous.