First off, the vast majority of ECU failures is not in the enthusiast market. The EMS, on the other hand, is in nothing but the enthusiast market.

As for the EMS being overkill on a mildly boosted Honda, boost is addictive, plain and simple. Anyone dropping the money and time to boost doesn't stay satisfied with a mild boost level for very long. If I had just a dollar for every time someone has come to me and said "I just wanted to be able to run 8psi daily, but now I want more", I would be quite wealthy. Spending money on anything less than the most you could ever possibly use is stupid. People that modify their car, and get a V-AFC, then decide that's not enough and get a chipped ECU or a Hondata, and then decide to take it to the last level and get a true stand-alone like the EMS, spend way more than they ever needed to. If your intention is to have a growing project [which most people do], then it makes absolutely no sense to spend "less money" and get only what you need for a certain stage of your project, because it just keeps taking "less money" to get to that next level until you get to the point where it would have been cheaper just to spend more money up front to get the best, be done with it, and have $400 more in your pocket.

I've built engines since I was 10, so I don't pay for assembly costs or anything like that, and I'm here to tell you that no amount of "skill" is going to let you cut corners on cost [both in cash and in time], and give you a reliable engine that makes lots of power. It doesn't happen.