Yes, getting a huge strong young guy on the ground is not going to be easy, especially if hes punching you. Not training takedowns in modern sport BJJ is a ridiculous oversight.
Even on the ground, pure grappling is different than grappling with striking. Then figure in if their big enough slamming you on concrete if you pull guard is also an option. Roll one time without mats on the wooden floor or with thin mats with less cushioning with one of these big guys, and add semi contact body punches and slaps to the face you might find it an enlightening experience.
I mean.... kind of agree? But not really?
At this point I have to ask the old and tired questions : do you train BJJ? Because I used to think EXACTLY that (and made countless topics on this very forum questioning BJJ in a real fight), up until around the time I passed two year mark of training and got my blue belt. Its at that point when I realized that I, a 36 year old former couch potato and exhausted father of 2, has zero issues completely wrapping up and immobilizing brand new guys that walk in that are way bigger, stronger, and younger than me.
I dont pull guard on them, I just sweep, mount, side control, or any other form of control that completely immobilizes their arms and head and body. They struggle and squirm but all they manage to do is burn themselves out.
Now where exactly in that 1.5 seconds it took for me to sweep them and immobalize them would they have had the world-class boxing skills to KO me or even touch me at all? In contrast to your gross underestimation of BJJ, I actually think you are WAY overestimating the average person's ability to throw a proper punch that does any damage at all.
It takes, literally, a split second to sweep someone into an inferior position. BUT herein lies my problem that I STILL question : we start rolls sitting down, in a real fight, how the hell will I get it to the ground?? THAT is where I am extremely deficient. In that case, I CAN easily get kneed or punched or KO right in the face, even against a clueless, flailing average joe.
And again, if you look at my post history you will see a TON of my posts and threads questioning the effectivness of BJJ in a real fight. This is not hubris or over confidence or anything like that, its just my simple, basic, clear as crystal observation from being on the mats day in and day out, against a vastly varied group of opponents of all shapes, ages, and sizes.