Verstappen was on average .3 seconds per lap slower than Hamilton, so back to reality. This has been the gap on normal sea level circuits since the start of the season. Verstappen was only faster than Hamilton on 16 laps, and Hamilton was up to 1.8 seconds faster on their fastest laps.
Reality rears it's ugly head, the Mercedes still has an ace up its sleeve. The car has more downforce, so can preserve it's tires better, it's better over bumps, and is faster in high speed corners. The power unit of the Mercedes is still ahead of the Honda, because the Red Bull has less peak downforce, it can just about match Mercedes acceleration. With less peak load the Mercedes would have the same straight-line advantage as Ferrari. Red Bull has to make a more extreme compromise, they are losing out in the high speed corners, and their suspension is almost as good as Mercedes. Where Red Bull does win out is in low speed downforce, they have bar none, the best car below 180kph. They can generate more downforce at a lower speed than every other chassis Mercedes included.
This means there's still an engine deficit, one being masked by a chassis that's very good at low speeds but compromised at high speeds. Honda has to deliver to tweak the RB15 philosophy into more peak load. With the tires being the way they are, having more peak downforce helps preserve the tires, but you cannot take advantage of the load without the engine power to overcome the drag. If the RB15 had the same peak loads and drag as the W10, Verstappen would be complaining about a lack of power.
The Honda engine has been getting closer, but it is still not yet at the level of Mercedes, and if Mercedes brings another big gain next year as has been rumored then Honda still has a mountain to climb. Honda is all in, and they are doubling down, so they must have some confidence that they can improve the power unit. No doubt the Red Bull 16 will be an evolution of this year's car, I don't expect big visible changes, noticeable changes yes, but they won't be miles off what's on the car now. Biggest changes will be under the skin, one of the reasons the Mercedes was so fast was the footprint of the bodywork behind the driver. They likely had the narrowest side pods and exits and that opens up the most critical aero real estate on the car.
The reason the big money teams and manufacturers win is because they make that area more compact than other teams(while respecting cooling requirements) can with their budgets. This opens up more space over the diffuser, which gives you more downforce. This area is the most critical area for downforce production on the entire car, and if you can get that right, you have more downforce in the back.(whether you can balance that out up front is another matter entirely).
This is why Ferrari, and Red Bull and Mercedes and McLaren tend to be up front instead of at the back. Well funded or creative teams can make headways, especially if said teams are inheriting the rear end from a manufacturer.
Teams like Williams are doomed to being backmarkers with their huge openings covering the diffuser so they can run their aluminum gearbox and cooling solution.
True the volumes are specified in the rules so you can't make the diffuser bigger, but you can remove structure from the path of the air, that void can let you duct air going through the body work, things you can't do if you fill it up with bodywork and cooling exits.
The height of cultivation is really nothing special. It is merely simplicity; the ability to express the utmost with the minimum. Mr.Lee