I’m with you - it’s really frustrating. Unfortunately, it’s a common thing with a massive organization like Samsung.
Keep in mind that SmartThings was originally a startup focused on smart home automation and focused on things like lights, locks, etc. Samsung bought them out and the big money for Samsung is their appliance business. SmartThings enabled Samsung to simplify the 50+ apps and backend platforms they had at one point into a single app to control everything. You still have each division doing their own device integration in some cases and they end up getting away with substandard stuff like that.
I’ve seen similar substandard implementations from third-parties like Cielo and you can almost excuse it since that third-party likely integrates with lots of platforms (and of course expect that they would ultimately fix it). But yeah, it’s surprising when it’s a seemingly ‘first party’ integration that is substandard. 
When you are in the modal, are you adjusting the “cooling” setpoint in that case though?
Since the thermostat doesn’t report the Thermostat Heating Setpoint capability or attribute, the modal shouldn’t be showing the heating setpoint nor the heating controls… so I would presume it’s just the cooling setpoint and cooling controls… and perhaps they are using the Cooling Setpoint as a proxy to actually set the Heating Setpoint.