A trustworthy certified advisor will save you time, money, and energy. A bad one, which is most of them, should be avoided at all times. A certified advisor may or may not save you money. At 1% of assets (not uncommon for an FA) - $10,000/yr per $1MM assets! Someone retiring with $1MM might hope to generate $40,000/yr in income using 4% SWR just for example - another $10,000/yr for an FA is relatively costly, and will have a considerable effect on retirement income over the long run. That's a pretty big incentive to DIY if you can. And your latter point is yet another reason to DIY, unfortunately "bad ones" prey on those who most need their services all the time.
Many people have never seen the difference using a CFP (not CFA, BTW) makes, for some people. I have, and I assure you, the difference a good advisor can make is substantial. For some people no doubt, my MIL couldn't DIY invest. This is a community of people who have consciously chosen to learn to DIY, so the poll and POV here isn't going to match the mainstream view - any more than preaching Hummers & Corvettes on a Prius forum.
Think of basic examples: many people change the oil in their cars. CAN everyone do it? Yes! SHOULD everyone do it? Maybe. I can't see my 84-yr old MIL doing it, can you? MUST everyone do it? Nope, and many don't do it either themselves nor go to a pro to have it done, they just drive as long as they can on gunked-up engines. And sometimes they break down on freeways and are put to a lot of trouble and $$$, but they want to risk it. Their choice. Paying $50-100 for someone to change my oil doesn't compare to $10's of thousands a year for a financial advisor.
You can write your own will. There's lot of books on the subject, free advice on the Web, legal forms available from many reputable vendors. CAN you? Certainly, and doing something is better than nothing, as I can tell from having settled an estate. SHOULD you? Again - maybe, and maybe not. Again, paying a (few) thousand for a complete will & other docs several times during retirement doesn't really compare to $10's of thousands per year for an FA.