These calculators do not model job stability. GP is correct to be concerned; unless they have a truly unique skill set in high demand for the foreseeable future, steady employment is not a given in many fields. In the US, one needs about 7 years to break even on house purchasing costs (all the fees and commissions outside the titular selling price) before it financially makes sense to buy into another/different house. This is why you hear the rule of thumb that tells people to rent unless they plan to stick around "for awhile", or "for about ten years". We need a forward-projected statistically-inferred probability, based upon historical trends of the field a prospective buyer is in, on their income stability for the next 7 years.
It should come out as at 100% of current income, 50% probability they will increase at rate of inflation over next 7 years. At 80% of current income, 60% probability. At 70% of current income, 90% probability. And so on. Then the buyer picks where on the gradient they feel comfortable, given any side hustles, investments, etc. they have going on in their lives. This balances out the traditional DTI ratio that entirely favors the lending side getting their transactional fees regardless of the actual projected affordability.
The younger generations around the world are getting completely shafted on real estate asset overvaluation, and many are right to be skeptical of conventional affordability calculations. In the US, there is the triple shafting of higher education, healthcare, and real estate overvaluation. Median asset values are way out of line to median incomes, and only supportable by an over-lenient and captured debt system. The reversion to mean will be painful, and unfortunately most of the pain will not accrue to those most responsible for the overvaluations in the first place.