Y'all caught me being less than rigorous in my language while posting from my phone while in the middle of making breakfast for the kids and the wife to get out the door. To the "not well defined" aspect, I disagree in part. There is an RFC for CSV and that is defined. Now the conflated part is the use of CSV as an interchange format between various systems and locales. The complexity of data exchange, in my mind, is not the fault of the simple CSV format. Nor is it the fault of the format that third party systems have decided to not implement it as it is defined. That is a different challenge.
Data exchange via CSV becomes a multiple party negotiation between software (sometimes the other side is "set in stone" such as a third party commercial system or Excel that is entrenched), users, and users' local configuration. However, while not well defined none of these are intractable from a software engineering point of view. And if your system is valuable enough and needs to ingest data from enough places it is NOT intractable to build auto detection capabilities for all the edge cases. I have done it. Is it sometimes a challenge, yes. Do project managers love it when you give 8 point estimates for what seems like it should be a simple thing, no. That is why the coding kata RFC compliance solution as a base first makes the most sense and then you troubleshoot as bug reports come in about data problems with various files.
If you are writing a commercial, enterprise solution that needs to get it right on its own every time, then that becomes a much bigger project.
But do you know what is impossible, getting the entire universe of other systems that your customers are using to support some new interchange format. Sorry, that system is no longer under active development. No one is around to make code changes. That is not compatible with the internal tools. For better or worse, CSV is the lingua franca of columns of data. As developers, we deal with it.
And yes, do support Excel XLSX format if you can. There are multiple third party libraries to do this in various languages of various quality.
As a developer, I have made a lot of my living dealing with this stuff. It can be a fun challenge, frustrating at time, but in the end as professionals we solve what we need to to get the job done.