This is a fair rebuttal. A quick google returns the following article from six months ago which presents evidence to show the current average overdraft of users of a debt charity is £1722.
Using Starling’s own handy overdraft comparison tool shows Monzo to be the cheapest at £15 over 30 days.
More expensive are (figures based on £1715 which seems to be the closest you can enter):
£17.87 First Direct
£19.92 Starling
£24.58 Nationwide, all the way up to
£74.90 Lloyds
It’s lazy, simplistic and anecdotal to simply say “Monzo’s overdrafts are extremely expensive”