I have one Classic Roman “Delphi” so it’s hard to judge all romans on just my expierience with her, but she tends to be calmer than most of my Toulouse, that doesn’t mean that she doesn’t have a spicy side to her though, I call her Delphi Dragon for a reason.
The Toulouse can be less level headed than she is, though they aren’t more or less “opinionated” I’d say than she is. I have a few Toulouse who are absolute mellow sweethearts, but geese are geese and even they get carried away if one of the other geese starts drama.
I can’t say either breed is necessarily safe around ducks. Some can be very friendly, other times they can be aggressive towards ducks, sometimes they can be too friendly to the point of drowning a duck while trying to mount it.
Geese are often friendly to ducks when raised with them, or if the geese raise the ducklings, goslings though are not safe around adult ducks, ducks from what I’ve seen do not like babies of other species, especially drakes.
Maybe my flock dynamic might summarize what’s more common in the relationship between ducks and geese.
I have quite a few geese and 4 ducks. Two of my geese lived with two of my ducks fine for a few years. Everything was peaceful until it wasn’t. “My mellowest gander Thor couldn’t stand the nightly duck porn fest going on next door and I had to separate them.” Currently the geese and ducks tolerate each other. They go about their business and ignore each other unless the ducks get too close and then the geese chase them away. The welsh harlequins are quick and get away just fine, Olaf the jumbo pekin has short legs and Henry has arthritis so I have to make sure they aren’t around them, especially in spring when Olaf is hormonal and tries to pick fights with my biggest gander Leo.
They do inadvertainly look out for each other, if the geese see something scary they set up an alarm and the ducks dive for the brush, the size of the geese seemed to be a deterrent for hawks, but that may not be true for all hawks. The geese can’t actually defend themselves or ducks from ground predators like foxes a larger.
The ducks will also raise an alarm if they see something which also helps the geese.
To put it in simple terms, they tolerate each other to a point and all the extra eyes benefits everyone.