It is true what is said about the better exit, at least looking at qualifying.

Hamilton was taking better exits out of corners and carrying that extra speed down the straight as evident in this onboard comparison w/ telemetry

...

We have the speed trap data and the onboard telemetry above which isn't showing anything crazy in straightline performance.

What lets you have better exits out of corners is downforce, and we can see that Hamilton's Merc was running a lot of that because it had what amounts to a huge barn door for a rear wing. All of that adds up. It makes sense.

The problem is that Hamilton didn't seem to be paying any penalty for that kind of downforce elsewhere on the track. That's not normal. You can't really clock at or near the top of speed traps all over the track when you're in that kind of a setup.

A new and juiced up ICE certainly helps, but it's not a silver bullet. You can increase peak power a bit by pushing the engine to the regulation RPM limit of 15000, abusing your turbo for higher compression ratios, and adjusting your ignition timing and fuel/air mixtures accordingly. Virtually every single time, this is also going to adversely affect your performance curve at lower RPMs so depending on the track the higher mode may not even be the best mode to use. Plus you're also locked out at 110kg of fuel per race so you have to average 50-75 depending on the length of the track just to get to the finish line. A higher mode with more power at 100% throttle is also going to be drink the fuel faster (within the 100kg/hr regulation limit), which means you have to make up for it by being a bit more conservative than usual elsewhere on the track. There is no free lunch here, at least not unless you've figured out how to violate the fundamental laws of thermodynamics.

Since the sensor changes, we can be pretty confident that Merc isn't feeding the engine above regs and without that kind of a violation it's extremely unlikely for the ICE to be the entire reason for Merc's performance gains. But that's why Red Bull is honing in on the rear wing. The most logical possibility is that Merc does have some kind of a makeshift DRS effect from flexing the lower panel at high speeds. Whether or not Red Bull can find definitive enough evidence of that in the Brazil footage is an open question though.