Thanks once again to everyone who responded to my questions. I just got back from India earlier this week; almost all of my flights were on time and I didn't have any issues anywhere.

Specifically, on the transfer from Gatwick to Heathrow:

I don't remember exactly if my flight was on time or not, but either way, it was not late by more than about 15 minutes. Once it landed, it got to the gate pretty quickly and I was able to rush past immigration and customs within ten minutes as I was not carrying any checked in bags.

It was a breeze locating the National Bus desk, and I was my own queue ;-) - the next counter (for trains) had massive queues, so I was glad that instead of settling back at the end of the queues, I went right up to the bus counter and inquired whether the queues were for the bus as well. The next bus (to T5, fortunately) was at 10:20 so I had a good forty minutes to kill. In hindsight, I might have been able to make it if either the flight was late by thirty minutes or I had checked in a bag or two (and waited 30 minutes) - but not both!

So, I got into the bus with a few other passengers and we breezed into the freeway going without any traffic. The lady at the counter had said that we would be in Heathrow in one hour and ten minutes. My flight was at 2:15 pm. So no worries at all for me; however, a family of co-passengers apparently had a flight before 1 pm (based on their conversation that I overheard).

And then we started hitting traffic, sparsely and far between at first, but as we got closer to London, it started getting thicker and thicker. Until, about 30 (projected) minutes to Heathrow, we stalled on the freeway because of traffic. Now I started to panic a bit. Slowly, we threaded our way through the traffic - my Google Maps app kept updating the projected arrival time at Heathrow. Finally, at 12:35 pm a full hour behind schedule, we rolled in. The family was not too thrilled as they got down and collected their checked baggage from under the bus. Me? I was not too worried, and strolled around for a few minutes taking photos.

Guess what? T5 scored better - for me - this time than ever before. Now, Orlando airport's typical 30-40 minutes through security seems absurdly high. I was through T5 security in less than ten minutes. No issues whatsoever in catching my flight to Bengalooru.

Thanks, everyone who replied!!