How do you intend to control them? Manually in the app? With a zigbee or Z-wave button/remote? With some other trigger like motion?
If you want to control a few lights as a group with a remote like the Aeotec minimote that’s pretty simple. Just use the built-in Smart Lighting smartapp.
If you mean you want to manually control them as a group I think you’re right that ST doesn’t make that as easy. But there are community-developed smartapps that are able to create master and slave dimmers (i.e. one dimmer changes and others follow automatically). Rule machine was one, which I use, but the developer withdrew support and the code’s no longer available. CoRE was developed by others as a replacement for Rule Machine, and while I haven’t tried it out yet, I’m sure it can do that. Both of those apps are pretty sophisticated rules engines.
There are probably also simpler, purpose-built smartapps out there for this purpose as well. I’ve used this one for a few GE link bulbs in my bedroom; I don’t know whether it will work for your Ecosmart bulbs. Try searching around the forums with the terms “master,” “slave” and “dimmer” to see what you can find.
If you don’t know how to install custom smartapps (I’m guessing you don’t from your post, since you appear to have just discovered the existence of the IDE, i.e. the website that you can login to and change various settings for your hub, devices and smartapps), check out the wiki created by this community.