No one is going to tell you mediocre academics will lead to an LOA. It might, if your whole person concept is compelling. Are a blue chip athlete, have a compelling diversity contribution such as underrepresented area, underreprented background OTHER than surface diversity measures (ie, do you work to pay the light bill? raise siblings? go back through my threads to the example of high schooler testifying about his dad's lawn business in bankruptcy court and getting cross examined.) The question should not be "Am I Competitive?" because that is essentially asking, "Am I like everyone else?" and everyone else = a rectangular lego sweating it out whether they are selected from one or more slates.
Instead, ask yourself what moves you on the continuum from competitive to undeniable? While undeniable is elusive and an idealize goal, asking yourself the hard questions is not. This is where I asked my DDs the 3 So-What's. For every line item in your resume, tell me about it and i'm going to reply, "So what? Every candidate has that/does that. What else have you got?" I'm on swim team. So what? I made states. So what? I am captain. So what? I am allowed to compete on my feeder high school swim team. I had to overcome logistics, established social/clicks, prove myself in the pool, to ultimately be named captain - of another high school's swim team. Ditto for other line items.
Back to academics, if you are on Plan B, ie mediocre or less than stellar academics, then be able to articulate how you improved and finished strong. No excuses. Yes but = yes but your competition did!