As far as ultra-Orthodoxy flourishing–sure. They do so by the support of their MO brethren, who receive an endless line of collectors for the ultra-Orthodox institutions.
BS”D
And those contributions are a drop in the bucket compared to how our own communities support Torah. On the other hand you may be referring to charedi institutions like Chai Lifeline in the US and Ezra laMarpeh, Ezer miTzion, Yad Sarah in EY and some Chabad and Aish organizations which actually help everyone no matter their affiliation and therefore are supported by all though most support comes from the more charedi sectors or from those whose physical communities directly benefit.
Indeed, unlike the more modern institutions, the charedi moisdos benefit all of klal Yisroel. When have you last seen a YU rabbi taking a meager paying pulpit in yenem velt and saving a few remaining Jews from assimilation? No, they know they’d fall apart out there and either wither because of lack of parnosso or even fry out because they can’t withstand the temptations of being in a small town where only a yarmulke that can easily be removed separates them from their secular Jewish neighbors.
You mention Rav Tendler. Don’t go there. No one is more known for compromising and even attack of certain charedi positions than he is. The failure of his derech is most astounding when it comes to certain people very close to him, vehamayvin yavin.
And most importantly, real MO is moving toward the right, with secular education being pursued for the right reasons only – parnosso. The Torah world will move toward this as well, leaving the MO of yesterday in the lurch – where they will either get with the program and remove the modern, or join kefira institute Chovevei (more like Chovlei) Torah and basically become the new CONservative.