The Married Person's Allowance was abolished about 5 years ago. As you've suggested, HMRC will still take the same amount irrespective of the date of your marriage.
I used to be a chorister in my (mispent) youth and there were always a lot of weddings just before the end of the tax year in early April. The other favourite time was half-way through the (tax) year in late September/early October.
The difference might have been depending on whether one or both of the bride and groom were working.
Or it might have been that people have always liked spring and autumn weddings!
I seem to remember that you got all that years or a % of tax refunded when you got married, that why it was always best to get married at the end of the financial year