The thread you’ve linked covers this topic in quite a bit of detail. To simplify it all down, your answer to 2 is yes, having more inertia will make the high wattage outputs (minimally) easier. However the trade-off is a trainer that is less responsive to changes in wattage, which isn’t such a big deal for sweet spot work, but is more of a problem for VO2Max and anaerobic workouts, which have larger wattage changes and shorter intervals.
The answer to 1. is … maybe. What will help you ride have sustained power on flat road rides is a higher FTP. I think consistent commitment to quality training will have a much (much!) more impact on your road riding improvement. Flywheel inertia is a very minute marginal gain (and I’d actually have to be convinced that it made any difference).