Riders who get picked up by WT teams get picked up because they are the better riders in their age bracket. So you think the world championships should by definition exclude the better riders. Which complety goes against the idea of a championship in the first place. Then they should call it "best of the rest championships". Or you want to entice the best u23 riders to stay away from WT teams and maybe go against what is best for their development, just so that in all likelyhood less talented riders can become world champion. Then what is even the point. Also, in the proces, draging the overall level down, as if the non-WT u23 wouldn't benefit from an elevated level. All the regular u23 would benefit from that, while alternatively only three regular u23 would benefit with a medal if pro riders are excluded.
I could understand if they brought the age cap for WT riders down to u21 our something. But i think it is a lot more unfair to have an 18 year old fight against riders over 4 years older.
Basically, you are watering down the competition, because by the time a good u23 is elligable to become world champion, he will very likely have been picked up by a big team.
In case he is levels above, he will likely race the pro WCC anyway, like Evenepoel did.