I just don't buy that argument at all. Tactics can be tweaked over time, and some tricks kept up sleeves, but if the WC is the be all and end all (and I'd guess to most of us it isn't) by this stage we should have a good idea of who the personnel will be, in team and wider squad, and the team should at least be coherent. Next year should just be polishing. The vast majority of a likely RWC team, especially in key positions like 8, 9, 10 and 15 should have at least 30+ caps by now - history shows experience counts.
Ref 19 RWC final, Sinckler didn't help but would have made precious little difference. We played our final the week before and were beaten up. It's difficult to get a team to hit those heights 2 weeks in a row, but Jones failed to do that despite an extra day's rest and he also admitted to selection mistakes.
Our attack was poor today. A bit of punch in midfield and a couple of decent wings would definitely help. But I'm actually more concerned about our pack which never quite seems to be the sum of its parts and not really intimidating - today wasn't the hugest of tests, we'll have to see how it stacks up v Ire and Fra.