If aviation fuel was taxed at 100%, the ticket prices would only go up 20%. This alone would not make trains significantly more competitive.

Generally speaking, though, it doesn’t make sense to compare subsidies and taxes individually. Both planes and trains are already heavily subsidized, and if you removed all subsidies and taxes, I suspect planes would win handily.

> if you removed all subsidies and taxes, I suspect planes would win handily

Until all transport is long-term sustainable in terms of environmental impact the cost calculus is messed up. Check out carbon footprint ranking of different modes [1].

[1] https://ourworldindata.org/travel-carbon-footprint

Hm, I wonder if the Eurostar to Paris includes the emissions caused by digging the tunnel.