The last vcftools release was in 2018. It has been superseded by bcftools for most purposes, and by plink 1.9/2.0 for most analytical functions which didn't get included in bcftools.
In this case,
plink2 --vcf subset_filtered.vcf.gz --make-king-table
is far more efficient than vcftools. I just tested this on a Mac on 10% of 1000 Genomes phase 3 chr21, and it took 1.1 sec using plink2 and more than 22 minutes using vcftools, even though plink2 was forced to waste time converting the VCF to its native file format.