If an alternative exists, I will listen.
Alternatives exist, just that these alternatives are many times not worth the time / money to develope. It's business, companies have to earn money, have to pay salaries and have to provide fast, reliable and decently priced solutions to clients.
A few years back, everyone was hyped up around Silverlight! "The Flash killed!" "All those C# and C++ professionals will wipe the floor with Flash!" "The huge developer community of Microsoft will kill Flash!" etc. etc.
... and where is Silverlight today? Exactly...
Competition is always welcome and I personally do hope that if not HTML5, then some other technologies will emerge and try to put some serious pressure on Flash. Doing so, Adobe might put more effort into smoothening out certain problems with the technology... "might". If they won't then hopefully the competitors will put the needed effort into their technologies.
HTML5 is in essente nothing more than HTML + Javascript ( yes, it has a few additional "special" components too ), but because browsers parse HTML differently, there will always be compatibility issues ( developers will have to spend N times more trying to fix browser specific problems than developing the actual solution... time which is translated into "wasted money" for the company or "higher prices for clients" ). Until HTML and especially browsers don't get their act together ( have a proper, accepted and consistent standard in place ), HTML will not be a viable solution for most companies that plan on developing complex / Enterprise level applications ( this is where "the real money" is at... not banners and bling-bling crap )...
Also more tools need to start appearing that support the HTML + Javascript development process in a "real" way ( there are a few now, but they are far from good or usable in large teams ) or at least some decent frameworks ( similar to GWT ) that can translate C/C++/Java/whatever and generate a proper HTML5 application.
... again, HTML5 still has a long road ahead.
Hopefully it will not end up as Silverlight did... only future will tell...