Yes, tubeless rims can be tricky to fit/remove tires. This can be true even with tubeless tires but it can be worse with tubed clincher tires due to risk of pinching the tube
With respect to your original post, I am in a similar boat: 28mm tires on a narrow rim, or 25mm tires on a wide rim, which one is better? Some of my frames have less clearance than your Roubaix, and most of them are set up with 25mm tires on 23mm outer width rims. They measure out to about 25-27mm true width. I might throw a 28mm tire onto a skinny rim just to see how it measures and feels. At the end of the day, I think what matters is the true width of the tire inflated on any particular rim, and setting the pressure accordingly. Obviously, need to make sure your frame can tolerate that configuration clearance-wise.