have you recently sensed the podcast taking a turn for the worse?
No, I have been listening since episode ~300 and it is on the upswing IMO. I watched both the Trevor Moore episode and the Les Stroud one and I don't agree with your criticisms.
The first 1/3rd of Trevor Moore was bad, but after the two got to know each other Joe let up and gave him more talking room. You act as though a lack of topics is the reason for quiet or awkward moments, it could just be a weird chemistry between Joe and the guest that has to be overcome. Trevor got in more than you are letting on. The dude talked for more than 30 minutes throughout the whole thing just about his vaping habits, and got Joe to vape through the whole thing. He had plenty of talking time for someone who appears to be more introverted than extroverted. If you aren't willing to watch the whole episode objectively you would certainly come to the conclusions you have made, seeing as they only represent the first part of the podcast.
The Les Stroud one is the opposite, the first 85% of that podcast was well paced and entertaining with only minor "Brian interruptions" (which I don't mind, I think half of them are funny and Joe is getting better at squashing the other half before they have time to breathe). The only criticisms I have of the last part fall short when I take into consideration the fact that they were drunk and it was after 3am when they had been up all day (and Joe just did a comedy set). They even made a comment about how tired they were and said that if you aren't willing to stay up late you wont have any crazy "stay up late" stories. Of course the conversation is going to go south and feelings are going to get hurt when they are drunk, tired, stoned, and then Les decides to go full retard. Joe was unwilling to accept the bullshit that Les was trying to sell him, and I don't blame him. It wasn't Joe's fault that Les suddenly took a crazy turn and started to get his Jimmies rustled when the others weren't buying it. I also highly doubt that the next day either of them had bad feelings for each other.
Again if you aren't willing to look at the whole podcast and instead only pick out pieces to decide whether or not the JRE is going downhill...you're gonna have a bad time.