I would also be a little nervous about relying in just a standard ceiling rose, particularly if I were not certain as to to how well it was fixed - but, in terms of what you say, the cover of the rose should not really be the primary thing taking the strain. In fact, wires pulling out of the rose (arranged per OPs photo) would probably be the least of my worries - I would be more concerned about the lampholder and the attachment of the rose to the ceiling.With a £600 glass table underneath I would not rely on just a standard ceiling rose where the cover is held by a screw thread formed in the pliable plastic that some roses are made from. Safety chain to a fixing into a joist is a good idea.
Kind Regards, John