I thought… “Even if I get a Patent, a big competitor can invalidate the patent with its large financial resources. So why patent?”
A patent right can be considered as a weapon to be used against a competitor as a sword (to attack infringers) or as a shield (as a defence if attacked by competitors). A patent is a strong deterrent against copying, but a competitor with large resources may attempt to get into your market by removing the only legal barrier against his move. So although a patent is not a 100% full proof defence against attack, it is nevertheless a strong deterrent against copycats.
During the period of market exclusivity enjoyed by you during the patent term, you should build the brand value of the patented product such that when the patent expires or is invalidated, the brand value associated with your product would help you to maintain your market share.