Maybe? I believe with enough traffic you can determine the actual content size by calculating the average apparent padding length. (Compare JavaScript timing side channel attacks that can remove random clock jitter, or Onion Routing traffic analysis.)

What you really want is padding to a fixed-length block. That requires restricting the maximum allowed length of confidential fields. (Could vary per field.) Yet such "arbitrary" limits have been frowned upon for ages as poor design.

That said, there's usually nothing stopping people from imposing their own limits and padding accordingly, server- and client-side. But without enforcement across the entire software stack it's difficult to maintain the invariant.