Should marching band control the direction and be the main focus of a band program? IMHO, no. With that said, most if not all of the kids love marching season and wish it could go on 24/7/365. Same thing with indoor percussion.
Use that to you advantage. Do you want your kids to be well rounded musicians? Of course, all of us want that. Use indoor as a "hook" to get the kids to...if not love the concert side of things...at least appreciate it at a higher level.