And this is based on your experience of using GOBLIN, or just hearsay?
I lived 5 mins from Leyton Midland Rd for 2 1/2 years (2014-7) and used the line every day before the long term closure. I can't speak for the daytime, but during the peaks 2 cars certainly did not cope! I lost count of the number of times I was left on the platform if I missed the peak time relief service (which doesn't even run anymore, so God knows what it's like now...). I suspect all of the disruption will have suppressed demand somewhat in the last couple of years but the passengers will come back when TfL finally get their act together.
The main issue with the buses was that they always got stuck in gridlocked traffic in Walthamstow. Hoe Street was always very busy, but the situation has been compounded by long term roadworks at the Walthamstow Central overbridge. I gave up on the rail replacements as they refused to stop at the last bus stop on Hoe Street, and simply took a 69 and walked the last bit into the station to save a few minutes.