I think that's off the mark and you can't really pin this on the batting capabilities of your no 8. India had the strongest top 7 in the tournament really and those guys have to deliver when it counts.
Look at SA with Jansen coming in at 7 and nothing much after that. That tail didn't stop Miller from scoring a 100 with a SR of 87 when he came in at no. 6. Even if you take the Aussies, Maxwell scored his double when they were 7 down for 90ish with only Cummins left with any kind of decent batting ability. These guys didn't care about the batting ability of the tail, they stood up when their team needed them, took the risks, played their shots and delivered when it mattered.
India's batting didn't work because they did not perform under pressure. Rahul and SKY struggled to get it away and Iyer got out playing a poor shot. Jadeja came in ahead of SKY to try and build an innings but he failed at that. Gill miscued one. All these guys are top players who can win games on their own. They don't need a number 8 to give them a safety net.
De Silva was on a radio station today morning and I was listening in as I drove in to work. Some of the questions centered around his 100 in the finals and also his knock in the SF against India. Not once did he talk about the batting ability of the tail giving him freedom in his approach or impacting his mindset on those days. His main comment was regarding on-field experience to deal with the pressure of the situation. In fact, I've found the clip online so here you go (he talks about it towards the end of this):
