Just listening to godly Em freestyle verses from the late 90s... what I noticed is this...
Then: he put every effort in to making every single line a knockout punch. It was ALL about the lines, all about the wit, all about what he was saying, line for line. He also put his all in to delivery, but his flow and delivery were secondary, it was about the lines.
Now: it's the reverse. Whilst he absolutely still does come out with badass lines, in recent times (and whilst I love flow and delivery experimentation / hope he continues), he's completely focused on dazzling with his flow and delivery, and the lines become secondary. If you think even of the "My Life" verse, it was more about those crafted bursts of flow and delivery he was focused on, and in doing that he cares a little less about the content, it becomes broader and he rattles off more simple rhymes "he's bugging / thugging" etc. where as back then, you didn't get any filler lines to accommodate flow. Every line was too precious. Every word even.
He still cares about lyrics, and definitely rhyming, but it's like he allows himself to get away with more, generic rambling to accommodate the nature of the flow and to try and dazzle in that department, it's more about how he's sounding than what he's saying. I'm definitely a flow/delivery guy though, but I hope for his next album he really focuses line for line.
I don't think it's that Em doesn't have the wit now, as I see many flashes of it and also many amazing moments of unique phrasing, but I think he's been SO focused on trying to innovate with his voice and styles that, that's why he may seem a little more surface with substance.