> I can't shake the feeling that Regexp could be written just as efficiently as a fluent interface with a more human friendly syntax.

You can use SRL - Simple Regex Language (https://simple-regex.com/) for making readable regex/matching rules. It is supported in C++, Java, C#, PHP, Javascript, and Python. Also, you can use the web version to generate equivalent regex if your language is one of the above.

Here is an example from the website for matching an e-mail address:

  begin with any of (digit, letter, one of "._%+-") once or more,
  literally "@",
  any of (digit, letter, one of ".-") once or more,
  literally ".",
  letter at least 2 times,
  must end, case insensitive

Regex to do the same:

  /^(?:[0-9]|[a-z]|[\._%\+-])+(?:@)(?:[0-9]|[a-z]|[\.-])+(?:\.)[a-z]{2,}$/i

The first one is readable, second one is cryptic. https://simple-regex.com/examples has more examples.

SRL was previously discussed here in 2017, see https://news.ycombinator.com/item?id=12384862

Also, the parse feature (DSL) of Rebol language is an excellent regex alternative:

1. Why Rebol, Red, and the Parse dialect are Cool (http://blog.hostilefork.com/why-rebol-red-parse-cool/)

2. Rebol's answer to Regex: parse and Rebol types (https://rebol-land.blogspot.in/2013/03/rebols-answer-to-rege...)