This is unfortunately not true. I just picked up this game and made 4 elves with the exact same attributes (17 str, 20 dex, 20 int, 14 will, 3 health). This started all of them off with 3 HP, 20 MP. I also set the game to Hard.

They each had different skills but acrobatics was held by 3 of them and the 4th was a shield user.
I started all them off with a full set of leather armor, minus the 3rd guy who had a pair of fur boots because he had to pick up a bastard sword for Theros. I needed to do this since Theros would be doing most of the early killing, because my party had to dodge until level-up since they only had 3 HP.

Upon spawning I picked Theros up and switched his equipment with the 3rd guy. So now my 3rd guy had a broadsword, medium shield, chain armor everywhere except for a pair of leather boots while Theros was using the third guy's leather armor, 2h bastard sword and fur boots. The other 3 had pretty much the same 4 pieces of leather armor and some extra weapons I got from creation to sell early.

I saved right before my party hit level 2 and I reloaded after every leveling, noting down my level-up points. Each time, I got random, different numbers in both combat and non-combat skills for all 4 guys and there was never any pattern I could recognize. Many times the member who used spells the most got the lowest Mana increase for instance, often times the shield/heavy armor wearer would get less health than the non-shield wearers etc.

I also thought that maybe the level-up points were split between HP/MP increase points and combat/non-combat increase points, so I added them all up and they were never equal. In fact, on one occasion one of my dudes got way more points than all the other guys, while most of them had 10 HP and 25 mana, he had a a whopping 21 HP and 39 mana, and he got a ton of skill points in both categories as well, above 17 anyway, while the rest lagging way behind.

Changing the difficulty didn't seem to help either. Although the manual says you get the most points when leveling if playing on EASY, I frequently got some of the worst totals per character while doing this (if we assume that 20 dex and 20 int would/should give you 40 points in total for both combat and non-combat skills, which is obviously not the case) I was frequently getting on EASY around 20 points in total per character instead of 40 or at least 30 something.

So TL;DR: leveling up is random/unknown and/or most likely uses some sort of archaic D&D RNG system, difficulty doesn't seem to matter much, you can reload right before you level to get better point spreads.