You’re right, native Glide Forms are somewhat lacking in data validation functions.
There is some basic data validation that can done at the component level. For example, with dates you can restrict the range to before or after the current date, you can set a range on number entry, and you can set a character limit on text entry.
For anything beyond that, you really need to use a Custom Form.
Custom Forms are a bit more work, but they give you much more flexibility, especially when it comes to data validation. The big difference is that data inputs are available in the data editor immediately, so you can use them to perform calculations and relate to existing data, and provide immediate feedback to the user - before the form is submitted.