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I don't think the commenter was intending to fund his purchase with a BTL mortgage - consumer protection laws apply to PDH docs and LTV covenants are seriously off market. So I don't think either of your links are relevant to this situation.
Also your last point is confused. What do you define as 'being a dick and overpaying', when your argument is that the market is overvalued. If you took that approach you'd never buy anywhere and would be renting instead, which is highly likely to be more expensive over the average mortgage term of 25 years, with less security of tenure.
you are wrong - margin calls can and do happen both at the end of the deal and sometimes, mid-deal.
http://www.housepricecrash.co.uk/forum/index.php?/topic/76232-margin-calls-on-buy-to-let-properties/&page=8
and read this case too:
http://www.bailii.org/ew/cases/EWCA/Civ/2016/491.html
the whole affair can be sensibly afforded by not being a dick and overpaying for the property in the first place - but you employ whatever technique you feel suits you best by all means.