One of the things that has frustrated me with O5e's move to separate ability score increases from, well anything, is that all of the species just become humans in funny suits. I do like removing the incentive to take a race just for mechanical synergy and encouraging people to play what they want. But I view non-humans as aliens. Even beyond the physical distinctions, they shouldn't see the world the same way. It's kind of funny because I realized why there is some newer 5e art (like in TCoE, look at p. 103 for a great example) that I artistically like but conceptually dislike. The reason is because non-humans are shown with very human expressions and reactions--humans in funny suits.
I expect WotC mostly removed racial ability scores reactively because they believe people want it that way for some reason (maybe the increasingly casual player base prefers humans in funny suits over role-playing aliens), with little detailed analysis of it. I'm assuming the Level Up designers put a lot more thought into it, so I'm curious as to what their reasons were. Is the intention to make everyone be humans in funny suits, or is that a side effect?
One way that could allow heritage/race/lineage to retain significance (ie, you're an alien) while still removing the gaming pressure to play the optimal combinations just occurred to me. What might work is if each race had racial features that clearly expressed their natural strengths. If a race is physically powerful, then it should have something like Powerful Build to indicate that. If they are especially Dextrous, or Intelligent, or whatever, they need some sort of trait that clearly spells that out. If all races had such traits, then ability score improvements could just be phased out in favor of a different form of stat generation.