Insufficient planning leads to ill-chosen and badly arranged content. Good design requires genuine talent and experience, not just a knowledge of a software package. Visitors need to feel confident that they can easily and quickly find their way around the site.
Web users are notoriously impatient.
Optimising the speed of websites is a job for professionals. Some of the worst websites have been constructed by a contact who has some technical ability. This is like expecting somebody to write and publish a good book just because they know how to type. Good websites are created by professionals with proven talents, proper training and relevant experience.