As someone with no axe to grind on any side of this debate - having never worked for TCX, TUI or Jet2 - I'll contribute to say I think Jonty's comments appear deliberately poisonous.
The Thomas Cook infrastructure was cobbled together through mergers and acquisitions over several years. The product - particularly in resort accommodation but you could possibly apply the same to the aircraft fleet - never could have the investment to reach the base standard that TUI has today. If TUI is unable to maintain the same level of investment for 2/3/4 years to repay debt, its product will by and large remain above that which TC was consistently unable to reach. That's before you get onto the discussion about cruise strategy where TC had nothing in-house but was a retailer for others but TUI has a big asset base through TUI and Marella which keeps operating margin in house.
If TUI embarks on an acquisition spree (although it's difficult to see what would be left to buy!) and saddles itself with further debt, the jury would be out on its long-term future. If they stick to doing what they're doing and develop organically after the pandemic, I see every reason why they should still be here. There is a market for what they're selling, and one that isn't exclusively defined by price - unlike the position into which TC steered itself over a few years before its demise.