This stat is kind of weird. Punctuality is defined differently in every country.
In Switzerland 3+ minutes delay is counted as unpunctual, while france needs a 15+ min delay. I think in Austria it is 5+ min but unsure. So these numbers aren’t really comparable because they aren’t defining delay the same.
In Belgium it's 6 minutes and only the arrival at the final destination is checked. Cancelled trains are also not included in the statistics, which has lead to trains being cancelled to increase punctuality: instead of starting it's journey 10 minutes late, the train starts "on time" 1 hour later. Travellers missing connections is also not included in the statistics.
So put these 3 together and the actual delays of travellers are much larger than the statistics would like us to believe.
And to add insult to injury, to increase their "punctuality", the train operator seems to increase journey times with every schedule revision. So not only are trains less punctual than they were a few decades ago, journey times are also often significantly longer.
So according to the statistics, Belgian trains are doing fine, but the actual travellers disagree.
No argument with the other points that you made, but I would much rather that they make the journey times longer and accurate, than shorter, but unlikely. Once a train is running behind and off-schedule, it only gets more and more late.
It's a cop out, a way to temporarily relieve the problem without actually solving the problem. Every year the trains run a tiny bit slower and every year reliability is as bad as the year before.
Especially for small trains and shorter journeys it has gotten silly imo. Journeys that used to take about ~15 minutes now take ~30 minutes. And at the time when it took that train 15 minutes, they were really punctual and reliable, while now they're not. I found an article from 2014 which remarked that Mechelen-leuven was going to take 26 minutes while it only used to take 16 minutes. Now in 2024 that same line is 25-31 minutes with an acceptable error margin of +6 minutes.
From my personal experience, those slower trains are not driving slower and being more punctual, they're just spending a lot more time standing still. My small commuter train to Brussels would always spend 10 to 50 minutes waiting in the same junction. In the case of the 50 minutes, I think it was just pretending to be a later train so that it could arrive on time.
running it slower on schedule does solve the problem of being more predictable and being able to plan a bit better if you have to catch connections. I much rather have more realistic timetables over trying to achieve overall shorter travel times.
The 'fast' version of Mechelen-Leuven (the 25min) is a lot slower now because they rerouted it to add the new Brussels airport stop on this line. Of course a train with fewer stops will run faster. But this airport stop seems worth it to me for both cities, though longer route it now runs almost the same time as the slow stops everywhere L-train (31min) between the two cities.
Anyhow, not really punctuality to blame in this example, it's a planning/routing choice. One you might disagree with, sure, but it's not punctuality.
Sometimes trains become "faster" in the same way because stops get skipped more often or cancelled altogether. They could run a very fast train between Eupen and Oostende, but what's the point if you're not picking up and dropping off any passengers along the route? Filling up the path for a "fast" connection almost noone can actually use. Trains in Belgium are slow in general because there are just villages and stops everywhere, every single train not on an actual highspeed line has the same hard choice: how many stops, where yes, where no, how many passengers a day does a stop need to be worth it? I've cursed often at the Beveren stop on the Antwerp-Gent line, but there are always people getting on and off there... Our city planning has just been shit for 200 years and this is a consequence, much of our rail network functions more like a large metrosystem.