Hey there and welcome to the TR community!
Distance and elevation are not taken into account – event types, however, cover just about every kind of event we’ve seen athletes prepare for. It all comes down to the energy systems an athlete needs to focus on to train for their race and the amount of time they have available each week to train.
For the gravel example, we know that gravel events are generally long and often a bit of a “grind.” To prepare for that kind of event, we focus primarily on aerobic power and sustained efforts – that means a plan that mostly features Endurance, Tempo, Sweet Spot, and Threshold workouts.
Next, once we consider the training zones we’ll have to focus on, we have to look at how much time an athlete has available to train. This will vary quite a lot from person to person.
With the event type and hours available to train determined, we can put together a plan that focuses on the energy systems we need to target for the race with workout durations based on available training time.
Do you happen to be training for a gravel event that will take about 6 hours to complete? If so, and you used Plan Builder to create a plan, I think you’re already on the right track. 
You can always check out our plans here (if you are signed into your TR account!) to check out what the workouts look like in the Specialty Phase, which is when training for your A event gets most specific. Gravel races will fall under the “Gran Fondo” Specialty Phase from our Road Racing plans. Here’s a snippet of what the Specialty Phase looks like:
It features a nice mix of Threshold work with some surges to help you stick with the pack during a race scenario, a sustained VO2 Max workout, and some long power work with the Sweet Spot session on the weekend. The rest of the remaining volume gets filled out with Z2 riding. Overall, a healthy variety of workouts that will help in prepping for a gravel event. 
As you train, Adaptive Training will ensure that you get the right individual workouts within your plan for your changing fitness levels.
Hope that all makes sense and helps clear up why we don’t specifically ask for distance/elevation metrics when building out plans. Feel free to let me know if you have any additional questions!