I've worked with two different dens over the years and will be working with a third. I have always made available the oportunity to earn all 20 activity badges. I believe almost everything can be presented in a fun way. For some of the dryer stuff, we did game shows style activities or homemade board games. Parent specialists were brought in to teach part or all of certain badges, field trips were taken. For at least half the badges the boys had to complete one requirement on their own and prove it. For example, for scholar the boys had to meet with their teacher and provide a signature. For family life I sent home a guideline with signatures needed by parents in several areas. Burn out, no, I believe it set them up for success or at least realistic expectations in boy scouts. Badges in boy scouts are not handed out to all who show up (at least not in our troop) the boys have to do the requirements and often have to do at least a few at home. In one den of motivated boys most of the boys earned at least 17 of the badges, all earned arrow of light, 4 out of 13 earned all 20. Of those 13, all moved on to boy scouts, 12 stayed over 1 year, 9 stayed for 4 or more years, 4 are eagle, 3 are life and 1 of those should reach eagle in the next few months (project is finished). Of the 4, 3 are still involved and one moved (unknown). The other den had a few motivated boys, but more were there for the social only. Although all earned arrow of light, 3 did not desire any beyond that, 2 earned 18, and 2 earned all 20. Only those who went beyond stayed with boy scouts for any length of time. I only see 2 who have the motivation to achieve eagle (younger group, so don't know yet).
I didn't know about or super achiever did not exist at the time. I created a den certificate for outstanding effort for the ones who completed 20. They earned it.