Grrrr, i typed up a bit reply to two questions then lost it when the page refreshed as i switched tabs.
Anyway, yes we’ve skiied Les Sybelles. It was ok, nothing special, we’ve never been back
Took the train the year, it was great and would recommend. Interrail is a question though, iirc you need to pay extra for the Eurostar leg and possibly for some intercity trains on the continent. Would advise checking on Snowheads as it’s been discussed there recently i think. On that note though, check this thread, you’re probably not going to get to Cervinia by train as a massive rockfall in the Maurienne means the Paris-Turin line likely won’t run till next summer
https://snowheads.com/ski-forum/viewtopic.php?t=165791