I think you’re being a bit harsh on Monzo here. I think they did have an idea of the volume of support needed, and they had planned for it, but they got caught out by circumstances unexpectedly overtaking the plans. There was some combination of growth being higher than expected, and recruitment being slower than expected. They’ve held their hands up and said that if they were to do it again knowing what they do now they’d ramp up recruitment earlier.
tl;dr, I think they knew, but just got caught out.
One thing I agree with is that if people have experienced support problems, and they don’t think they can vote for Monzo as the best bank because of that, then that’s absolutely the right thing for them to do. I think it’d take quite a Monzo zealot to disagree with that one (and I hope that most of the most dedicated ‘fans’ on this forum are still not that zealous).
Personally I still think Monzo is the best bank account and would vote as such, but given I have been adding the “Support isn’t optimal at the moment, so don’t go all in just yet…” caveat when recommending it to others, I can’t fault anyone for thinking otherwise.