Not an OG, but a One X here.
I have been getting some frame-rate lag on Ultra Graphics (PC-style fully customizable graphics quality on console included) during some of the Campaign mission, including the tutorial Wallace Campaign.
That said, the lag is only really when moving the cursor around the screen.
There is no lag (that I have seen) when you keep the cursor static.
In random map, the One X get this same frame-rate lag on fully visible maps over Large size.
Like I said, this is One X.
The OG will likely have a worse experience, but keep in mind that I am playing on the highest graphic setting.
Either way, as a GamePass title, I’d say its worth trying out anyway