No, it is not a defense and a judge will not allow it to be argued. You're lucky the DMV were slow in issuing the suspension since, when stopped for running the light, your car would likely have been impounded if the cop in that stop found your license had been suspended.
It's also not a defense to a failure to appear to say you forgot.
You knew about the FTA ticket because you signed that Citation. That will be enough for them to show Suspension. You need to hire an attorney to get the best plea deal possible.
Seth Weinstein, Esq.
Los Angeles Criminal Defense Attorney
This reply should NOT be considered a legal opinion of your case / inquiry. At this time I do not have sufficient factual/legal documentation to give a complete answer to your question and there may be more to the issues you raised then I have set out in my brief reply.
The best way to deal with your ticket is to clear the previous citation and get your license. You can argue all you want about your lack of knowledge- but taking care of your previous matter will get you the best results. Get an attorney to deal with all matters.
Andrew Roberts (818) 597-0633/ (805) 496-7777