The limits of a gravel bike are the speed, Terrain they can cover, the comfort tire clearance and weight.
Gravel bikes combine features from road and mountain bikes and also have wider tires for off road use and an upright seating position.
Gravel bikes also require more maintenance and wear faster than road bikes.
Gravel bikes are also designed to be robust and can also be heavier than regular road bikes and a high end gravel bike can weigh around 18 lbs to 20 lbs and a cheaper regular bike can weigh 22 to 36 lbs.
For some people gravel bikes are not as comfortable as a regular bike or mountain bike with front suspension and gravel bikes are also slower than road bikes when road on paved terrain and are slower than mountain bikes when rode on off road trails.
Also gravel bikes aren't designed for the biking trails that are the most challenging and riding the gravel bike on deep sand lanes or steep root carpets may not go to well on a gravel bike.
A gravel bike also has less suspension than a regular bike, making the gravel bike faster on paved roads.
However, the gravel bike also has more tread on the tires and a sturdier frame than a road bike, giving them more stability and comfort on unpaved paths.
A gravel bike also has a taller headtube, steeper headtube angle, and a lower bottom bracket.
This makes the gravel bike stable mostly in a seated position and optimized for minimal tech.
Most gravel bikes also don't have a suspension fork or shock.