Well, Merckx didn't enter the 1967 Vuelta - I'm assuming a mistype as what you state refers to the 1967 Giro, but by that time we already knew he could handle recovery within one day's racing (he'd already won San Remo twice) and the stages he won were stages 12 (finishing at Blockhaus) and 14, so we knew he could handle recovery within a Grand Tour, so bearing in mind he was not yet 22 at that point, I don't think anybody in their right mind would have said there was anything missing from the toolbox for him to win a Grand Tour. If anybody was claiming him the favourite for the 1967 Giro, people would have rightly been saying to pump the brakes until he'd proved he could do it over three weeks.
Remco has not yet demonstrated the recovery that Merckx showed in that 1967 Giro that put the final piece of the puzzle together in terms of the weapons at his disposal to win a GT - in his one attempt at a Grand Tour he faded badly after week 1, but it's also not really a representative performance in my opinion because of the circumstances of that Giro regards his injury, crashes, illnesses and so on. He may well be able to do that now that he's been able to target a Grand Tour without the injuries or disrupted preparation he had before - but we haven't seen it yet. Merckx's stage wins in 1967 were after more days' consecutive racing than he'd ever done before, whereas Remco's is on stage 6 - we know he can do it in one week, it's whether he can replicate this type of form after another week and a half of racing that is the only real remaining question.
Regarding Vine, as a late starter the most significant deficit I think is likely to be in pack skills, the fight for position in the péloton in the stages unsuited to you that comes with trying to do a high GC placement. For the moment it's probably best for him to stagehunt with no pressure on maintaining a GC position. Pack skills are an underrated requirement of top level pro riders, as there are certain riders who will frequently get caught up in crashes in the bunch, or miss splits in the péloton, and similar, and once in a while it's unlucky, once it's a pattern it's a problem. Some riders like David Moncoutié would always sit right on the back of the péloton and accept that he'd miss a split in the bunch if it happened, but he was happier to be there where it was safer as he could see everything going on around him.
Facebook
Twitter
Instagram