I think the best should go head to head all the time, like in many other sports. F1 is often taken as an example and there all of the best ones go head to head all the time. Many other sports are similar and I cannot think of a sport that does what cycling currently does where the best can go full season without facing each other.
The OP said it would kill cycling. I do not agree. The sport would be changed for the better.
He can train well for a lesser race and get spotted and get the chance at the TdF the next year. It is not like Castrillo happens every year.
I do not agree. It is those teams that make the race anyway.
Meintjes could be a dom on one of the top teams.
There is some danger in going downhill, especially of you are chasing a group. I understand that danger is there and that is part of the sport. However, crashes like Basque or at the Tour with Rog are the ones I would like to be avoided. And those could be with smaller fields.
F1 is absolutely turgid and boring as a spectacle and has been for years. And I say that as a motorsport fan. Also I'd point out that actually, the best ones don't go head to head 'all the time' in many sports. There are plenty of sports where they
theoretically could, like swimming or athletics, but where the athletes set their own calendar around certain bigger, more important events, they often prioritise big events. Hell, take something like cross-country skiing - there are plenty of 'the best' taking place in every race, but there are also discipline-based specialists who run a selective calendar and only enter certain races.
You say something like Castrillo is a rarity, that it doesn't happen every year, but it used to happen every year
and then some. Take 2009 as an example. Pro Continental teams (the then equivalent of ProTeams) won TEN stages of the Giro d'Italia (di Luca's two have been removed, but one of them has been given to Stefano Garzelli who was also a ProContinental rider). Even if you remove Cervélo who were to all intents and purposes a top level team, there's still seven. Guys like Petacchi, Scarponi, Garzelli were all lining up for ProContinental teams and, crucially, rather than it being just another World Tour race, this was their entire year. Other riders may have been planning for the Tour, but for these guys, this was what their entire season was built around. None of these guys were going to the Tour or the Vuelta, so they went all-in for the Giro and enlivened it.
Now let's go to the Tour, and the 2009 Tour so one of the most dominance-friendly designs ever, with easy-to-control mountain stages and a long TTT that had a hugely disproportionate impact on the GC. Even there, Brice Feillu won the first mountaintop finish and wore the polka dots for a few days before Franco Pellizotti and Egoí Martínez' battle took it over. Cervélo were a wildcard team there too, and won a stage and the green jersey with Thor Hushovd, plus another stage with Heinrich Haussler. Then finally we have the Vuelta, where despite it being a pretty tame race throughout, one of the few things to enliven it was the ever-trying, albeit less than effective, Ezequiel Mosquera for Xacobeo-Galicia, because, like those Italian teams, he had built his whole season around the Vuelta a España. He would end up 5th on the GC, his teammate Gustavo César Veloso would also win a mountain stage on Xorret del Catí, and the team would win the Teams Classification as well after putting two men in the break that was allowed to gain 20 minutes or so on stage 15. Andalucía-Caja Sur would be limited to pointless breakaways for a second straight year (they had won a stage in 2007) but that was largely due to GC candidate Xavi Tondó getting injured in the stage 4 pileup. Vacansoleil made their GT debut as a wildcard team and won a stage with Borut Božič, and finished 12th on GC as well as being extremely visible throughout with Johnny Hoogerland.
And the thing is... that was
normal. 5 of the top 10 of Milan-San Remo were on ProConti teams (two of which on the podium, but they were Cervélo riders). 3 of the top 10 of the Ronde were (one of which was Cervélo). Only one (Haussler) at Roubaix, but 2 at Liège (one Cervélo) and 2 more (neither being Cervélo) at Lombardia.
Of the eight biggest road races of the year in trade teams (the three GTs and the five Monuments), nine out of 21 ProContinental teams could contribute a top 10 finisher or a stage winner. And there were guys like Pozzovivo, Visconti, Tondó and van Hummel in those other teams too.
Nowadays, all those guys would not be racing to make the best of themselves and enlivening the races they targeted. They would be riding as domestiques for the riders better than themselves, and trying to actively
prevent any enlivening of races. I'd like to see
fewer World Tour teams and
more wildcards, so that races can have different flavours and some good riders end up in teams where they need to go hell for leather for a smaller number of targets a year, rather than seeing five guys who could be leaders for other teams all riding in service of another guy who's already won 25 races that year, because not only is it better for their bank balance, but it's better for their own GC ambitions to come 5th being Jose Azevedo or Yaroslav Popovych to a modern day Lance than it is to come 5th being Ezequiel Mosquera or Domenico Pozzovivo.
Frankly, to me, that's not progress. That's a crying shame.