AWS: Application vs Classic Load Balancer
1) you are using 2 classic ELBs instead of 1 ALB
so costs savings can be a factor

2) using a layer7 loadbalancer vs a layer4 gives many features and capabilities not possible otherwise

you can see a comparrison here: 
https://aws.amazon.com/elasticloadbalancing/details/#compare

3) yes that wildcard would fit all your needs (sub1/sub2.domain.com)