I completely agree with you that the entire consumer ESS industry status on interoperability is pretty dismal. And I look forward to better standards.. I may be naive/overly hopeful, but I'm hoping that things like the power control system certification, once updated (possibly couple of iterations) will effectively require a level of interoperability (or better yet, and industry agreement on a secure communication standard for ESS and related components)
HOWEVER,
Your comment strikes me as more of a caveat emptor situation, than a legitimate vendor complaint. It is not fair to a vendor to complain when purchaser didn't research, or check for, a requirement in advance, purchasing a low-cost DIY product, and then whining about something not being there that they want.
It is perfectly valid to complain when something that is supposed to be there, either isn't or works so badly as to be unusable/worthless.
But to want something you weren't willing to research/pay for... in the IT world, the acronyms ID10T, PEBKAC, and the like are used to describe such behavior/people.
For customers who 'have a life', the answer is simple - don't go the DIY roll-your-own route. not yet anyway, not this early in the technology product lifecycle. I won't be surprised if it is another 5-10 years before easy interoperability between residential ESS components becomes mature, robust and common place.
Properly coding an interface, testing, thorough exception coding and testing when trying to interoperate with equipment that may, or most likely is not coded to a mature quality level, is expensive. End-user support for that interface is a LOT more expensive. And there are products that do this, and they are, naturally, as to be expected, a lot more expensive. Sort of like the old Project Management saying, "Good, Fast, and Cheap, pick 2"
https://en.wikipedia.org/wiki/Project_management_triangle [For those into modern Project Mgmt lingo, replace Good, Fast, and Cheap with Scope, Schedule, and Cost... same thing] You only get all 3 once something simple/limited in scope is VERY mature and optimized