You can’t fail TAC! Give yourself a break. You have said that TAC has proven to be no more successful for [you] than [your] past attempts at learning guitar. Is that not a Win?
I have said the same thing here multiple times before, and I know that many others concur. Of course there are thousands of TAC members who are inactive, that is really the only way to not progress in TAC. Some of them are perhaps making progress on their own or with some other help. It isn’t the only thing out there but I think it’s the best because it keeps you coming back day after day.
TAC is all about giving your best 10 minutes to the challenge and then marking it complete. If you have time and you are still enjoying the process then add on more time. We don’t pass or fail daily challenges.
It’s about finding things that went better today than in the past, it’s about sharing your wins with like minded people and encouraging others who share theirs.
You are not alone in having doubts and most of us started TAC not understanding how to approach it. I think it would be well worth your time to read through this thread from last year: https://tonypolecastro.com/family-forums/topic/wondering-if-i-should-stay-with-it-or-not/#post-2150460