Not exactly comparable. Flash, at its height, had pretty much the "multimedia in browser" market cornered with draconian vendor lock-in effects. They didn't need to hurry that much with fixing issues, because what are you gonna do if you are not satisfied with the Adobe Flash plugin? Run your favourite Flash game with Microsoft Silverlight? Use the open-source plug-in that could only run some Flash 1.0 animations?
At least with browsers you can easily switch vendors (the whole point of standardization and techs like WASM), or even fork your own.
Even if I don't like Apple or Steve Jobs that much, I must say they did one great thing killing off Flash by not allowing it on the original iPhone.
Oh, and guess what? We now have no browser competition because all the relevant parts are in the Flash Player and good luck motivating Adobe to fix issues with it now that it's basically a requirement to run a browser. Oh, and now they could charge everyone to access it if they want.
I want to live in your world!
Same arguments can be made for Flash: Plugin's developer can fix it without waiting for browser. Disable the plugin and use the same browser.
Conclusion: makes no difference conceptually.