I don't think we know if his takedown defence has improved though, there's not really a great deal to back that up since the Mendes fight. Aldo was a flash KO so we never got to see how that one would have went. Diaz basically stood with him in both fights and when it did actually go to the ground in the first, submitted him. Alvarez I believed went for possibly two takedowns in their fight and they were in the second round when he'd just been dominated in Round 1 and clearly had nothing for McGregor on the feet, more desperate attempts to get him down. We've not seen him tested in that department since the Mendes fight. There's no doubt he's improved as a fighter since then but it's tough to say how much his wrestling has improved since that fight because he hasn't needed to use it or really defend a great deal of takedowns against a high level wrestler.
Mentioned a year or so back about how I also think his willingness to be so open defensively on his feet is one of his biggest weaknesses. It led to him eating a good amount of shots against Mendes and two wars against Diaz, he even got caught heavily when KOing Aldo. He's clearly got a damn good chin though but nobody so far apart from Diaz has really been able to take advantage of how open he is on his feet. It's a unique style, he's so confident in his own striking which in fairness he's absolutely lethal with.
It's why I'm seriously hoping they do the right thing and have him defend against Khabib or Ferguson. You can't go wrong with either. Khabib provides that top level wrestling challenge which would answer big questions. Whereas Ferguson is one of the few guys around that has a style just as unique as McGregor, can take punishment and comes in at absolutely crazy angles with unpredictable offense. While I've mentioned I think McGregor is open on his feet, in fairness it always makes for great fights, always entertains. I'd personally prefer Ferguson for the first shot, would likely be the most explosive build up for a McGregor fight ever too, Ferguson is a nutter.