To put it simply, there's no good reason to replace Vanadium with Cromite on GrapheneOS : you'll get the opposite of a better browser.
I tried the desktop version of Cromite on Arch but removed it because the only clear feature for me is disabling JIT and you can do that on Chromium/Chrome by disabling the V8 optimizer, also note that Cromite is almost 100% written in C++ which is a memory insecure language with a ton of attack surface. So I preferred to go back to Chromium via the official repository which works fine for me.