Okay Helwig, let's talk.
"I can fully accept the theory that training with the gi will tighten up your defense and escapes for fighting. Just as no gi makes your offense better by having to deal with a slipper opponent and using overhooks and head control rather than grabbing the uniform."
Here's the thing. I've tried to present this idea to many no-gi practitioners, but they are so deeply seeded in their training routines that they bypass the simple logic that I am presenting. I've done a ton of research on this subject including interviewing many of the top BJJ guys in my area in gi and no-gi and this is what I have come up with.
Instead of getting in to a debate of "who trains gi and are they champs?" vs "who trains no-gi and are they champs?" argument ----- I'd rather spend the time giving you reasons why I think training with the gi is beneficial....Even to the MMA fighter as we share some of the same goals.
1) When you begin training with the gi, especially from a no-gi background, do not let the "humbling process" (as one guy deemed it) deter you from continuing to learn.
Let me explain this a little bit further. In the beginning, whether you have been training no-gi for a long time or not, you will get caught in submissions that you can normally escape. It's because of the obvious added constraints to the scenario.
2) Use MMA techniques while rolling with the gi on. For instance, instead of grabbing the collar, go for head control. Instead of grabbing the sleeve, go for a grip on the tricep, etc. If you train with a no-gi/MMA mindset, you can really develop a tight jiu-jitsu game when it comes to MMA.
3) As you stated earlier in your post, your defense most certainly will go way up. Your awareness of submissions escalates dramatically. You can literally feel when someone is going to go for something. The fact that you have already been rolling for a long time will only help you in this quest to better yourself.
4) When you are applying submissions or escapes, the extra grips that others have on you will greatly reduce the ability to power out of a bad position or a submission. Instead, you must rely heavily on employing fundamental techniques in order to escape a bad position or a submission attempt by your opponent. This will sharpen the most important aspect, IMO, of BJJ. Which is DEFENSE. Without defense, you can have sick submissions, but can hit a roadblock in success because you are always in bad positions or getting subbed yourself.
5) The application of submissions also gets sharpened. For example, I rolled a little bit no-gi for a while before I started training jiu-jitsu and one of my favorite subs was the RNC.
I noticed that after training with the gi for a while, I would sometimes struggle to get the submission in because my training partner would have more grips to grab on to when I was trying to apply it. This constant defending of my sub, made me practice my timing more as well as the actual submission itself.
A few months ago, I was rolling no-gi and when the opportunity presented itself to apply a mata leao (RNC), I slid it in so effortlessly and instinctually, that I actually surprised myself.
This could be due to several factors, including practicing the submission more as well as more time on the mat. But I definitely know that practicing the move with a gi on greatly assisted the process.
6) Training with the Gi is not an end all be all decision. It's more of a supplement to your training sessions. If you train BJJ about 4 days a week, break up the week to training 2 days with the gi and 2 days no-gi. This change-up can also keep things fresh and will reduce the chance of getting bored or burning out.
----> There's more if you are interested.