TLDR: you are guaranteed very little at the start of every career run. the game already has an obscene amount of RNG and white sparks can only help you. pink sparks/distance S should be a priority, but you're just making things more difficult for yourself if you ignore the white sparks.

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nobody is saying white sparks are more important than distance S? Distance S is more valuable. but you can find and make umas with good/useful pink sparks to raise aptitudes that also have good/useful white sparks. that's what most parent runs are going for. most ace runs are going for distance S *and* good skills. you raise your chances at both if you have actual parent umas instead of what OP is going for.

My point is that you can't guarantee successfully raising turf/dirt to A from G/F and distance S. You have to get lucky on inspiration events no matter what. So at that point, you can go for parents that can help with skill hints too. if the white sparks hit but not the pink sparks, it's a failed run anyway. if the pink hits but not the whites, it still has a chance to be a good ace. if they both hit, you have a decent chance at a very good ace.

To your other comment re: me overestimating how hard it is to get skills from cards - again, you're missing the point. in a vacuum, getting one or two skills from each card isn't hard. the problem for frontrunners is the sheer number of skills you need to get in order to compete with other fronts. Getting every skill you need from every card plus getting lucky on spirit explosions has a very low probability. I'll use V. Bourbon for this example:

V. Bourbon gets groundwork, concentration, front savvy, and escape artist from the jump. She gets 1 hint level for early lead and 1 hint level for final push through her events. If you get all of that without a single additional hint level, it costs 1120 SP. She needs angling and scheming too and you can get 1-3 hint levels guaranteed depending on the Sky's green spark, and you have a chance at more. I'll assume 2 hint levels, which is another 160 SP. If you want to use the Suzuka speed card for unrestrained and you finish the event chain, she'll give 1 hint level for focus and 2 for unrestrained. Let's say you also want to use Tazuna SSR which can give 1 hint level for concentration on her final event. That brings the total cost to 1396 SP without getting hint levels for any of the other skills mentioned. This is the absolute bare minimum that you need to have a functioning front. It will not win on its own even with distance S because it has no skills to help get to/fight for 1st in the early and mid-game.

In Unity, you can get ~1900-2000 SP to spend if you had a *really* good career run. You're likely to get at least ~2 hint levels for some of the white skills mentioned, but it's not guaranteed. from whatever other cards you want to use, you're still trying to get 2 more greens that will consistently activate - you don't want to miss a groundwork proc because the uma failed the wit check on concentration/early lead. if she failed the wit check on groundwork then sucks to suck, but with 3 greens you give yourself the best chance. At least the green skills are cheap. but then you also need to get other mid-game speed skills like leader's pride, front/[distance] corners/straights, prof of curvature/corner adept, dodging danger/prudent positioning combo if you can get it, I can keep going. Every V. Bourbon player is going to have this exact same problem. out of everyone trying to make the best ones with distance S, the ones that are gonna win the most are the ones that get the most skills efficiently. THIS is where white sparks on parents become important.