instead of using modifiers species ought to lean more into having a longer list of various more granular traits to portray their strengths and abilities, these traits ought to cover and influence a vast array of gameplay scenarios so that they come up often, only having a few niche situations where your choice of species affects things is half the problem in characters just feeling like humans IMO.
so instead of +2 DEX a halfling should just have innate advantage on stealth rolls, not because they've been trained but because the fundamental halfling physiology is adapted for subtlety and passing unnoticed, and you can still have your 'the clumsiest halfling' with -1 stealth, but stick them next to the clumsiest human or gnome or dwarf who all also have -1 stealth and they're going to come out ahead because that's just what halflings naturally excell at, and then they should also have like 7 other things that being a halfling influences about them, they're lucky, so they've got their rerolling 1s, but also maybe increased crit range 19-20, they resist fear effects, their small size lets them pass through other creatures spaces and hide behind them as well as just giving a flat +2 bonus to AC, halflings don't leave blatant trails behind and so are harder to track, maybe they could have very discerning palettes and can detect if food or drink has been tampered with or can reverse-engineer potions ingredients by tasting them, and maybe they have extrodinarily good memory for names and faces so they gain a bonus on those kinds of checks.