Yeah true, it was a little inconsistent then - teams seemed to dominate for a period and then be supplanted by a completely new team for a while. We saw that at times in the 80s as well - Serie A in the 80s might well be the strongest most competitive league ever, at least for a good number of years in that decade.
I think it's just splitting hairs really - I do think it's less competitive now, but I am probably overestimating the extent of that AND I am willing to admit I might be mistaken by looking at different league tables from the past and comparing them to the present. It's really the concentration of player talent in teams like Messi and Ronaldo's Barca and RM respectively, and Man City in England, that has given me that impression. As well as the top five leagues powering away and leaving traditional powerhouses in smaller leagues with nothing (Ajax, Benfica etc). You could even argue this happens between top 5 leagues - the decline of Serie A is shown in the decline of Milan and their paucity of CL winners since 2010. However, Zidane's days were hardly the 70s - they weren't long before Messi and Ronaldo and the Bosman ruling (the key thing in less competition since then) was already in effect in the late 90s and early 2000s so overall you're very likely right and I am overselling the respective gap in competitiveness between eras.
As for his position in the modern game - I think he would have to play as a number 10, but with so many teams playing 433 now the playmaking number 10 seems like a more rare thing. I am not sure a player like Zidane really fits into the modern game, with its obsession with pressing, athleticism etc. Of course when he got on the ball he could destroy teams. Like you say he was sluggish and seemed slow (though I'd argue he was a master at making the game play at his speed, like the best players tend to be). I think in this era with the athleticism he'd maybe find it harder. But in terms of talent he'd be second only to Messi in this era. But there's every chance he'd be a misunderstood genius. To be fair this goes even more for a player like Riquelme, who really did need an entire team built around him to get the most out of his passing and playmaking game.
Anyway, jamrock thinks we shouldn't be debating this here so could maybe ask a mod to move these posts to the Zidane thread?