I absolutely agree with you. On-page and Off-page SEO, when executed perfectly, definitely improves website ranking. And when your website becomes visible on top, you will get more traffic. The more traffic to your website, the more opportunities you have to generate qualified leads, to nurture and help solve users' problems and ultimately sell your product or service, gain a new customer or client, and continue to grow your business.
Yes, proper SEO strategy will always give you a proper result. If you can implement your on-page and off-page SEO properly then you will rank for a longer time. Quality backlinks will also help you to hold your ranking for a particular keyword.