The PLP need to be able to choose their leader, because that's their day to day job and they need a leader that has the confidence of them in parliament to win elections. The electorate choose their MPs in the first instance via vote - that's democracy. OMOV means you just get reactionary infiltration of the voting system and you end up with stupid leaders like Corbyn. Arguing something is only democratic if everyone has an equal vote at all levels is silly - it's like saying there should be a referendum on everything instead of votes in parliament.
The fact is the weight of vote importance should be geared towards the PLP.
Not that it matters, as per usual the unions and membership have torpedoed it and give themselves yet another punch to the face. It's amazing the amount of self-harm Labour has done itself in the last five years. And, of course, that's the problem now - people don't trust them and see them as a bunch of ideological incompetent morons. The stain of Corbyn will take years to wash off, if it ever does, and the Tories have free reign in the interim.
The PLP do need to choose
their leader, but the problem the party has is that (though this is much better now than it was from 2010-2019) there were an awful lot of people in the PLP who were, frankly, at best useless and at worst snakes. Let us not forget that the likes of Austin and Woodcock got peerages for what they did, with Hunt, Watson and Dugher ending up with jobs that at least have the appearance of being sinecures. Then there was Danczuk, a man whose Parliamentary career took in almost every scandal possible.
These were not people in whom anyone - party member or otherwise - should have put any trust whatsoever, and all of them had power and influence within the party (fortunately not any more). Even the people who you could at least make an argument left on political grounds - TIG - demonstrated how bad they were at the basics of politics. Remember that memo where they plotted to absorb the Lib Dems? Or when they blocked a possible Brexit compromise deal?
Or to put it another way in 2015 the PLP put up three candidates and they proceeded to get thrashed. The electorate would have given any one of them a similar kicking; they were terrible and fought campaigns (Burnham's especially) that really should be studied as examples of failure.
Then the PLP then got to the point of having an overwhelming anti-Corbyn strength in 2016 and could have just told him he could remain Labour leader, but that the PLP would appoint a Leader of the Opposition that enjoyed its confidence. They'd have had Parliamentary sense and logic on their side (given that Corbyn probably wouldn't have even been able to form an effective government unless in a landslide win) - but no, they proceeded to pick an even worse candidate than the 2015 mob. He then got thrashed. They'd still have got thrashed in the event that their hypothetical LOTO faced a general election, but at least you would be able to say they understood how the Parliamentary system worked.
The PLP between 2010 and 2019 were, frankly, a disgrace who could not be trusted with anything. Leaving them with choice of party leader would have probably killed the party. In 2015 the membership - correctly - tried to do something about them.