I find it impossible to replace a legacy system without first understanding the legacy system. It's easy to say "X is old" or "X sucks at Y" but keep in mind that applications have a strong survivor bias. Ask yourself, "what does X do that is awesome" or "how has X lived this long" and you'll find a lot of hidden scars and requirements.
Start documenting those requirements and create a plan to map those to technologies that you prefer. Understanding how to successfully migrate platforms is a learned skill, and it's going to become useful again when React is no longer en vogue.
Start documenting those requirements and create a plan to map those to technologies that you prefer. Understanding how to successfully migrate platforms is a learned skill, and it's going to become useful again when React is no longer en vogue.