It absolutely is. That's what happens. The party that won a general election will always choose a leader that way.
I'd accept opposition to it from a moral high ground more if the same people who refused to accept the biggest electoral vote in history and spent 7 years crying about it and the people who object to parties appointing new PMs wasn't a Venn diagram that is essentially one big circle.
I also haven't heard you mention this point in respect of Miles v Gething which is going on now and in the country we live in.
Obviously questioning our democracy to make a party political point is less appealing to you in this instance?!