Yes, his effectiveness as shown by the numbers has remained the same (reduced a lot the past two seasons, but bumped back up this season to just below the old levels - looking at UCL stats). But it's important to remember that because of his loss in agility and explosiveness, and his increased experience, strength and maturity - he does not attempt the difficult dribbles like he used to. That's why the sample of dribbles from now is collectively a set of easier dribbles than the ones from a few years ago. And Messi still had better accuracy then. That goes to show that he was definitely a better dribbler, or atleast showed it to the world. Just look at this video below, and notice how he squeezes into the smallest spaces between the lines. Of course, there were a lot more inefficient dribbles in there but that's kinda irrelevant as we're talking about skill in dribbling.
I have a somewhat similar "feeling".
I haven't checked the stats and this is hard to measure, but my feeling about Messi aged 20 and Messi aged 28 is this:
-- aged 20, he would touch the ball, let's say 20 times per match
-- and out of 20 touches, he would pass the ball to a teammate 10 times
-- and 10 out of 20 touches would be dribbles
-- so, imo, he attempted dribbles more often compared to a total number of HIS touches
-- also, in the past, whenever he decided to dribble (in those 10 actions), he didn't think too much and didn't care whether there is 1 or 4 defenders around him
-- so, when he decided to dribble, he would just tried to dribble past 4 defenders, if needed
Today, 28 aged Messi:
-- he is slower
-- he isn't that fast in acceleration
-- he weighs more
-- he is not that fast in changing directions, in little turns and moves as back then
-- but, he is much "smarter" and more routined now
-- for example, today, if he has the ball in the 3rd minute of the match, he won't run like an idiot through 4 defenders
-- there is "no hurry" for something like that
-- and he will dribble only when he see "a lot of free space"/when it is the right moment
-- or, when we are losing and we need some magic, then he will dribble past 4 defenders, if needed
-- also, I said that I have a feeling that he would touch the ball 20 times in the past, and tried 10 dribbles out of 20 touches
-- but today, he touches the ball more often as he is our key player, so let's say that he touches the ball 30, 50 or 100 times per match
-- but he still tries 10 dribbles
-- now 10 dribbles back then is on paper equal to 10 dribbles today, but in total, he touched the ball much less back then, and today he is our key main and a key man in a build up, let's say
-- so, in the past he would tried to dribble more often compared to his total number of touches
-- also, today he passes the ball much more to left and right to his teammates, and he waits for "a perfect moment to dribble"
-- while as a kid, he would dribble (almost) whenever possible
-- also, in the past, he would often try insane dribbles through 3-4-5 defenders
-- while today, he will dribble only if he has to dribble 1-2 opponents before he is able to make a shot on goal
-- today, he will do "insane" dribbles against 4 defenders only if we are losing or if he is extremely playful that night
Again, that doesn't mean that he is a worse player, but he surely is different.
He plays more with his brain, and he waits for a right moment to make a 50 meter run/with dribbling through 3-4 opponents
-- while 7-8 years ago, he wouldn't hesitate, save his energy and similar, and he would run in 50 meter solo actions almost whenever possible
So, I agree that it is hard to say that 5 dribbles per match today are exactly the same as 5 dribbles in 2006 or 2008.