The format will have some questions on whether it's any good after this tournament. Your arguments against the buy are mostly valid such as nerves, not being used to equipment and the expectations being high. However, being warmed up is a matter down to them. Sure, Swiss Stage warms up your stage performance, but at a professional level, you should be able to warm-up before any match to have that mental arousal in-game.
As for not being used to the new meta in officials, anything can go right or wrong on the day on-stage. Teams will have been scrimming for hours a day to adapt to the new meta and develop a new playbook for their comps. And you have to remember that there was a solid 2-4 weeks buffer time from the Stage 1 grand final - of course, you can argue most teams won't be using all this time to develop strategies, but there is nevertheless ample time to practice new things.
The meta is actually so open now so anything can work as long as you have confidence in the agent synergy. It's not like certain teams are late to the party in going with the meta since anything can work if you have success in your scrims using a certain comp.
Lastly, the fact that #1 seeds can pick their opponent is a huge advantage since they can VOD review their opponents on every map they play in swiss to develop an anti-strat. 4-9 maps of gameplay is quite valuable to base your veto especially if you've got a deep map pool like G2. Serot mentions XLG trolling their pick and on paper it is what it is, but XLG have a bigger issue where they lost their key flash initiator player. YOU's assists and util to set up Rarga was actually huge and that's something that cannot be replaced easily. I feel bad for them since YOU left/was released for allegations from years ago (matchfixing which he upheld his ban for back then).