The Consulate's strategic goal have never been conquest of Imperial territory, it has always been to rein in Imperial expansion.
I've always thought the 'magic rock at Rhylanor' was just plain dumb. It was too pat, too simplistic, and too childish. Yes, the Zhodani are deeply concerned about the Insanity Wave, as well they should be. The wave will wreck the vast majority of the Consulate decades before it hits the Core-most of the Imperial border and this leaves the Zhodani incredibly vulnerable.
It's my opinion based on my study of history the Zhodani strategic goal for the 5th FW is to push the Imperium back to a line of Aramis, Rhylenor, Mora, and Trin's Veil Subsectors, giving a 2 subsector deep buffer zone so that the Consulate can deal with the Wave effects without Imperial interference. I also freely admit that this is a desperate hope and a damned thin thread to hang the fate of your society from.
I also don't think that a simple 'one stab at Rhylenor' tactic would do anything but waste the strategic initiative. The Zhos didn't 'catch the Imperium on their back foot', the caught the Imperium with their boots all the way off. In order to successfully establish the buffer zone they believe they need, the Consulate has to reduce the Imperial naval presence [that is, engage and destroy the Spinward Marches Fleet] and destroy the naval bases and shipyards capable of supporting such a fleet in 8 subsectors of Imperial territory. That is a mighty big order. The Consular Navy has been training its officer corps for just this task for the last 5 or 10 years. Meanwhile the Imperial Admiralty, convinced of its own supremacy, has been eff'ing around with social politics in the officer's mess and relying on dated tactical and strategic thinking. To be blunt about it, the Consulate may never get another chance as good as this one to stymie and deflect Imperial expansion.