I don't think you are missing much. It is do-able, particularly if the traveller can use the e-gates to exit Schengen. The walking distance may not be far and even a 15 minute delay is not necessarily Game Over. But it's a lot riskier than a 2 hour connection and things like bus disembarkation can really slow things down. I wouldn't count your EC261 gains, TAP hasn't got a great reputation for easy payment and bad weather can cause many delays in any event. It's more likely you'll just arrive late into GRU.