I never said that and don't claim that is the case
I know, but let's further elaborate on WC and Olympics routes to see the actual winners and what they did to prepare:
2008: Sami Sanchez - Did the Tour, won the OG. WC, can't remember the race, but I don't think anyone was beating Balan/Cunego regardless of the Vuelta
2009: Evans Competed Vuelta for GC
2010: No GC rider was beating Hushovd with the headwind, don't think doing or not doing the Vuelta would have matteed.
2011: Even more so.
2012, Noone was beating Gilbert on his favourite hill, regardless of the Vuelta and he himself won 2 stages there.
2013: Nibali, Purito and Valverde competed in the Vuelta for GC, were beaten by Rui Costa. Would they best him had they prepared especially for this race? I don't think so, totally racing situation.
2014: Didn't watch and can't remember the route, but judging by top 10, not suitable for GC riders, hence with or without Vuelta not much of a difference.
2015-2016-2017 unfavorable routes for GC riders. Again, Vuelta or no Vuelta = no impact.
Olymipcs 2016, admittedly no GC riders competed on a favourable course, bar Nibali, who wasn't doing the Tour for GC, but again non of the top Tour GC riders at the time was notable one day racer.
2018: Valverde did the Vuelta for GC and won against riders specifically targeting the race.
Admittedly his Vuelta wasn't great.
2019: Not a route for GC riders and with the conditions, the Vuelta had no impact.
2020: Interesting route, GC riders had a chance, Pogacar was active and attacked, Roglic was in the group contending for Silver. I don't think he would've achieved more had he not rode the Tour
2021: Olympics, top 10 we only Tour riders with Pogacar and Carapaz competing for GC, Van Aert winning all kinds of stages.
2021 WC - not a favourable route for GC riders, the Vuelta didn't have impact.
2022: Evenepoel, we know, won both
2023: Heavy Tour for Pogacar, yet won a medal on a route not great for him.
2024: OG, Evenepoel destroyed both races after competing for GC
2024: Noone was beating Pogacar (okay, I still think he was beatable, but that's a different discussion), O'Connor was second in the Vuelta and won Silver, Mas.. competitive on both.
2025, Admittedly the Vuelta riders didn't perform well, but again most of the top GC riders in the Vuelta weren't notable 1 day riders, so I don't think they would perform better regardless.
As you can see, the times that competing a GT for GC before the WC/OG has a negative impact compared to a specific preparation are mostly exceptions,