Welcome aboard giveacar. There are several camps of thought in this area, each with their own fierce proponents, each with their own drawbacks.
Yours is one of the client views, that you should be able to manage your own content, and it should be easy to do that, you shouldn't have to be "computer geeks like us." Fair enough, but it comes with consequences.
A program you purchase is worthless without sufficient training to know how to use it, and use it well. I am one of those that particularly cannot stand Front Page or it's permutation to Expressions Web, for the very reasons you state here - they sell it as an easy, one-click solution, but as you've discovered, it is not, and can ruin someone's hard work with the click of a publish button. All of these programs, marketed as easy solutions, are this way.
Note that this is not a "slam" of these programs (I have other reasons for slamming them, but they are not these) as in the hands of someone well trained they can produce beautiful work. What bothers me about these is they are marketed as "easy" site solutions and in reality, without sufficient training, they can do much more harm than good.
The second option for someone in your position is what is called a CMS, a Content Management System. These are programs you load on your site, and via a login you make changes to the pages. They generally comprise of a template, the framework for your site, and the elements - page content, etc. The advantage here is you can't "break" your site as easily, you have access only to the content itself. Most of these are FREE, you just need someone knowledgeable enough to set them up.
The problem with these is that those who would harm your site also have access to these programs, and often abuse that knowledge to figure out how to hack sites using them. A weekly occurrence around here is "my site was hacked" and a lot of that can be tracked to use of open source CMS programs, and of course, ignoring the suggested security practices.
Last is my opinion only, don't take it personally. The Internet has trained us to seek out and implement anything we can for as little as possible, and to cut out as many agents as possible. Your agents - web designer, backend developer, SEO guy/gal, whatever - can help you and are there to help site owners succeed. Sure we have families to feed, and as you are now discovering, simple things are nowhere as simple as they seem. We only make it look that way.
If more clients would stick to their agent's advice, include agent fees in their budgets, let us help you succeed, in the long run you spend a lot less money and frustration getting where you need to be. So overall, my suggestion? Let your developer handle it.
Second choice to that, get off E.W. and use a CMS.