Some people are using The Noonlight service. @heythisisnate helped them create a SmartThings integration so it could be used with his Konnected product, but my understanding is you can also use it just with smartthings and not with connected if you don’t have any wired sensors to include.
It’s still cloud-based, but if you’ve been happy with scout and understand the vulnerabilities, it could be a candidate.
However… it only works with the classic app, not the new app. And they’ve already told us that the classic App will be going away eventually. So you might end up with having to change it again sometime later this year. 
There are other people who have given up trying to integrate security tightly with smart things and just gone with abode or ring alarm. Abode has more features but costs a lot more. Ring has limited features, but is really inexpensive. You would have to buy new equipment in both cases, but again, ring (owned by Amazon) is a very inexpensive security system.
You can get some partial integration with both either through IFTTT or through some custom projects that people have done, but it’s pretty limited.
Abode: Integrated cameras, allows you to arm/disarm based on Geo presence or time schedules, Can use some of the same devices as smartthings but only specific models and is limited to 160 devices total and 100 automations total.
Ring: Can only arm/disarm with the keypad or the app. It’s zwave, but requires S2 support and only the newest devices have that. So it’s unlikely you’ll be able to repurpose anything from your SmartThings setup. Although ring also makes cameras, they are not well integrated with the security side. That could get better in the future, but I always buy a Home Automation or security system based on what it does today, and not what they say they’re going to do. 
Anyway, it’s just basically a very low cost but decent quality security system with optional professional monitoring.