First off - great projects, welcome, and keep making sawdust! Amazing work after just 6 months...
Second - about MDF - the structural properties of wood and MDF are pretty well known. And you were following the plans you had. However, MDF - especially low density MDF - is much weaker (3-7 times) than most solid woods used for furniture and I've never seen MDF used for legs in this manner. I'm sure your table feels sturdy, MDF is relatively heavy, and it will certainly hold up for its intended uses. However, it's the unexpected stresses that can be most damaging. Someone sitting on it, or a leg being banged (hard) while moving could have damaging consequences - these things can be stressful even for a solid wood leg.I don't know if it will be less structurally strong, but who knows?
You seem to like Arts and Crafts type designs. Might I recommend some additional resources - to expand your collection of books and plans. There is full-blown revival of interest in this style, plus it especially appeals to many woodworkers, so there are many resources available.
I like many of the Tauton Press (Fine Woodworking) publications:
In the Craftsman Style
The Fundamentals of Woodworking, Volume 1 (actually 3 books)
The Essentials of Woodworking series
- which includes Practical Design Solutions and Strategies
The Furniture of Gustav Stickley
Any books about Greene and Greene
Darrell Peart's website - http://www.furnituremaker.com/