Are gas stoves preferred in a commercial kitchen due to having a constant heat source
Commercial burners generally have a high power output. A commercial kitchen doesn't have to be large to have 12 burners, all capable of 3kW, in a small space, plus ovens, and running near constantly. By this point the cost saving of gas over electricity becomes significant (in the UK, electricity is about 3x more per kWh). In addition many premises wouldn't have sufficient electricity supply to support that in addition to all their other consumption, and running a fatter cable is very costly. 

Only induction gets the pan up to cooking temperature as fast as gas, and although it's getting cheaper, it's still expensive to install. I've seen induction wok stations used for food that's cooked to order; one advantage is that they need less extraction than gas (but still some).

The pulsing you mention isn't really an issue. The fairly thick aluminium pans used in many commercial kitchens, and the large thermal mass of food being cooked would tend to minimise fluctuations in the temperature of the actual dish

Many of these reasons don't apply at home, but many of us prefer gas anyway for its controllability (at least compared to mostelectric stoves, I've only cooked on induction a few times and fairly simple stuff).