Thanks for taking the time to give some feedback and don't worry when it comes to discouragement; if the least bit of critique would blow me out of the field I shouldn't be here and I wouldn't last a month. ;-)
For sure you have a valid point, and for people who have an intermediate knowledge of computers and learning new software / platforms (and that want to save money), those are good alternatives. Reasons why those alternatives don't really bother me:
It is already way too advanced for a lot of clients, most of which have no clue what HTML or CSS even means. A lot of our (or my client's) clients rather spend time on their food, hairdressing or whatever it is they do, and feel like their time is more efficiently spent that way.
Customizing looks easy but is still relatively limited if clients have a specific / custom idea.
Nothing is really free. As soon as you want to use any of those programs to actually send out the e-mails, they have fairly low limits and will cost you money afterwards.
Those are templates, and just that. What we will offer in addition: List management, Custom signup forms, autoresponders, additional automated emails, surveys, feedback and suggestions, editing / searching visual material.
Maybe I should've included this in my main post, as I should take into account that the average Reddit user is way more tech savvy than your average small business owner. From the current client I work for we have some testimonials (video) from the clients explaining how our services helped them increase their turnover by a large amount which I am allowed to use, but I'm hesitant about this since the video is edited in the same old-fashioned / unprofessional way I specifically don't want to portray us in, and names the other company a few times (although this can be edited out).
I have to mention that I will avoid focusing on companies which I think are more than suitable of doing this on their own, or which I feel will need to constantly be convinced about the value of our services. A lot of companies know (or are easy to convince) about the value of e-mail marketing, but are tech-scared or uneducated. For those companies, a full service where all they have to do is come up with an idea and approve it once we made the design is an interesting service which I think will only get more attractive with further developments in terms of e-mail marketing. The templates you mention are (or will be) part of our process, but will remain just that, a part. Hope that clears some things up.