Just safer, not necessarily faster
OpenWRT addresses directly the chip and, yes, it may lag behind for some recent chips, but usually they catch up over time.
Moreover, I trust more the OpenWRT team when it comes to writing code. Router companies may advertise x or y, but the reality is often different.
In addition to that, OpenWRT allows you to bypass the limits set by the manufacturer (e.g. actual power of the chip in dB / W, security options,
And, maybe not all but some routers have some "convenient" features that share some of your bandwidth with "special" functions that usually you don't care about.
Then, sure it's not pure speed but the fact that you can ssh the router and install tons of modules is so convenient...
Don't worry though, in about 6 months
You are very optimistic regarding his or the government life expectancy, whichever comes first.
What is now proved was once only imagin'd. -- William Blake