Napoleon getting captured definitely contributed to the negotiations in Schonbrunn being much less harsh and might have helped Staps get a good shot on him, but Austria was still beaten down by the remnants of the Grande Armee. Hell, I think that encapsulates how big the Grande Armee really is. You could have a lunatic commanding it (as they did while they fought to get Napoleon back) and it'd still win due to sheer size.
Aspern Essling turned out to be a big mistake. The crossing of the Danube without enough secure bridges combined with the spring melt was a stupid thing to do. Davout handled it better a few weeks later and secured a brilliant victory over Archduke Charles in almost the same place at Wagram in July.
The Schonbrunn Parade was a tragedy waiting to happen. Stapps was motivated, as he confessed prior to his exrcution by the spectre of Napoleonic rule over the Confedertion of the Rhine States, Napolon's lst words "You cannot kill a sect with cannon balls confirm this.
It would be true to say that Ger,man and Italian nationalism would have led to unification sooner or later but, had Napoleon lived perhaps his would have been achieved with less bloodshed
On the oher hand some have argued that Napoleon would have been defeated sooner or later. Perhaps a German War of Liberation led by Austria and Prussia. However, it is hard to see how this could happen given the Russians were pretty firmly alled to France in 1809 deploying a Corps of Observation which ended up seeing no action. Napoleon was certainly not foolish enough to invade Russia. Had war with Russia ever come Napoleon would have fought a defensive war as he did in Bavaria in April 1809. Joseph of course was no general and left war to he very well qualified Davout.
Indeed, when war withRussia fnally came in 1812 Davout stood on the defensive in the Duchy of Warsaw and crushed Kutuzov's invading armies in a campaign even more brilliant than Napoleon's 1809 Bavarian campaign. After that, even the new Lord Liverpool administration realised the futility of an expensive and unwinnble war with FranceSpencer Perceval was assassinated by the deranged John Bellingham who thought he had a grievence aganst the government, ironically over compensation over his alleged unjust imprisonment in Russia. During the 1812 Polish War he Prussian generals Yorck and Blucher attempted an uprising. Tjhat of curse resuled in the removal of the House of Hohenzolern and the Partition of Prussia between Bavaria, Saxony and the Duchy of Warsaw, all firm French allies. As a result of the Partition the Duchy of Warsaw became the Kingdom of Poland in 1813