No it's most definitely not state of the art. Here is the state of the art:

http://nlpprogress.com/english/grammatical_error_correction....

Rule based systems are currently mostly a fun curiosity, but can also have niche uses e.g. for under resourced languages or for establishing a baseline for a completely new task. The most recent open-source rule based grammar checkers I know of were created using Constraint Grammmar at the University of Tromsø https://victorio.uit.no/langtech/trunk/langs/fin/tools/gramm...