Do you have some evidence for that? Do you see a lot of innovation coming from, say, China, a place where intellectual property rights carry no weight? Why no, no you don't.
China? Of course. They have been innovating for centuries. Long before patents ever existed.
As for evidence; the entire course of human history until patent law, even in its rudimentary form, ever existed.
Simply put, patents do not spur or encourage innovation. Necessity does. Always has. always will. Innovation is about creative problem solving.
Would a pharmaceutical company, for example, spend millions (billions?) developing and testing a new drug only to see a competitor instantly clone it and sell it for less (no R&D to recoup, you see) due to a lack of patent protection? Hardly.
With the profit motive as the underlying paradigm, they mostly seek to solve the most profitable problems meanwhile discouraging less profitable, and in many case, more effective solutions.
Patents protect and encourage innovation. That said, the patent system is broken and needs a major revamp. Patents themselves, however, are necessary and an important aspect of the capitalist system.
Patents simply protect profit or profit potential. Nothing more. Humans around the world innovate every single day. That's how our lower primate ancestor evolved into the Homo Sapien species. We are creative problem solvers. And having an opposable thumb goes a long way toward effectuating problem solving.
As for patents being necessary in a capitalistic system, I disagree, in part. It's only necessary to the degree in which it is most beneficial towards materializing the rewards of the profit motive. It's an incentive system that unfortunately stifles the invention/innovation of less marketable solutions for the public at large. There are many less marketable solutions that fall by the wayside or are skipped over simply because there isn't or wasn't a presently "justifiable" profit to be made.
Patents are legalized monopolies. Worse still, the majority of patents have a scope that is too far reaching. That aspect is responsible for patent trolls to exist and to pursue "similar" ideas. Further, patents substantially increase the risk of innovating. Something which retards innovation. Too close to a "similar" idea or were not able to do due diligence in research if a patent already exists in a reasonable amount of time and you could at best incur an unaccounted for expense. At worse, go out of business.
So where do I agree? I agree that in trying to avoid potential patent infringement, one has to be quite creative in solving that particular problem. You could deem that as "innovation." But that mostly leads to inefficient use of resources and time.