How can you not?
It's like anti roll bars and solid axles. The 2 designs are completely different
Hard corner for example, outside wheel is pushing up on the chassis
Inside wheel pulling down
Creating a twisting motion. If a brace is bolted it allows the strut tops to move independently but limited, loosely like an arb
If the brace is completely solid they can't without stretching or contracting the brace like a solid axle. Another comparative item is a roll cage, welded cages are much better for chassis rigidity than bolted ones because (other than bolt failure and safety) allow articulation
Either way the effect is dramatically reduced in cars like ours with the strut tops so close to the bulkhead, it acts like a brace already. An mx5 on the other hand is another story
