He's kind of right. Im not 100% sure if Icefrog cant balance or not but there are glaring problems that he is neglecting to address. Carries should need at least 2 items before they can start dominating teams. Currently, the popular carries need only 1 big item or 2 medium items to pretty much win the game. Lycan needs vlads and BKB before he can win the game. And since hes the second fastest jungle other than enigma, he can get these items in under 20 minutes, before teams have any type of viable response.
You can look at morpling. All he needs is an ethereal blade to pretty much oneshot supports, and has such a strong early-game that hes pretty much a 0 compromise hero. At least Lycan can be delayed by constant ganking (Delayed, not stopped. I have tried this many, many times. Lycan farms so fast and needs so little that unless you are ganking him the entire game, he will eventually get his cores). On the other hand, Morpling has ridiculous early-game potential with his 300+ damage nuke/pseudo blink and str gain, making him nearly impossible to gank.
And then there are heroes like Windrunner, Furion, and Brewmaster, which need serious rework/nerfs. They just offer way too much at every stage of the game and have absolutely no concept of checks and balances. I dont think I need to go into detail why these heroes ive talked about are so good, and if you are sure that they are not that great, you are simply kidding yourself. The professionals you adore agree, and hence these heroes are banned or picked constantly. They dont do that because they like their models; these heroes are extremely powerful, fit every playstyle and meta.
Icefrog is okay at balancing; its not an easy job. He's had some balancing fails, like Spiritbreaker, and some genius ones like the Invoker rework (Seriously, such a slight change yet he feels so balanced now. Powerful, yes, but not auto-win anymore).
He also needs to take into account trends; for example, AA was considered 'overpowered' by those who didnt know much about balancing (the vocal minority). With almost no changes, thsi hero kind of dropped out of the top pick/ban, ironic considering his anti-push was considered broken, and we are currently in a push meta. Hes still a great, balanced hero who fills a niche.
Which brings me to the next point; niches. This is a topic i think Icefrog needs to address; as long as there is a hero who performs much better in a given role than another hero, Dota will never be truly balanced. As long as Leshrac does everything Gyrocoptor does except better, Dota will never be balanced. Heroes who serve a certain niche should both equally be considered, and one should be picked other the other given circumstances and situation, not because the hero is simply better.