Married filing separately is a filing status of last resort. You really only want to do that if you'll save a ton of money through PAYE. Financially you'd be better off not getting married in these cases.
Apparently you can file separately in order to not take spousal income into account, then file an amended return to make it joint instead without recalculating the debt relief. Seems a bit shady to me, but apparently not uncommon.
Yes it is better not to get married in such a situation. At least financially speaking. But it is still false to say spousal income is always taken into consideration.