“Add in lethal techniques to multiply the effectiveness of your counter
takedown by orders of magnitude. Even when you are fighting off your back,
there is no reason you can't use lethal techniques.”
You can use what ever technique you want, but you need a base from which to operate. On the ground, the base should be BJJ. I have been involved in martial arts for 20 years, including TKD, karate, JKD, kickboxing, wrestling, judo, and more than 13 years in BJJ having earned a black belt. You have no idea of how helpless you would be on the ground with a BJJ black belt and the same is true of takedowns against a very good wrestler, or striking with a very good kickboxer.
I really don’t think that you will find anything more lethal than a choke. You have 3-5 seconds to get out prior to passing out. I know that you are thinking that you will just grab the groin or attempt an eye gouge to get out. You won’t have the time or the opportunity to do so.
You have to train in these areas to be proficient. You can not just train different ‘scenarios.’ How many ‘scenarios’ could happen in real life? The numbers of possibilities is unlimited. I think that you should get good in each range and then if you want to add in lethal techniques, then feel free.
The reality is that if a good boxer decided to eye jab, then he would be able to do so more effectively because of the skills he developed in timing, power, etc. The same would be true of any other range of combat. The person who sepnt more time training there will have many more options and a greater advantage.