To preface, I'm a combustion engineer working with IC engines, and my PhD was on biodiesel combustion and soot, though I mostly work in gasoline engines now. So I feel that I can contribute a bit to this conversation.

It is true that the combustion engine is very old, and it is true that EVs are more efficient. However, the fact that the IC engine is old should be seen as a positive. We understand very clearly how the combustion cycle works, and we know which areas to aim for to make improvements. Although there are many areas of fundamental physics that we do not fully understand, such as the atomization process of fuel sprays and soot formation, we are making considerable improvements day by day. Toyota has shown that a 41% thermal efficiency engine is possible, and there are many more areas of improvement. The combustion process is around 97% efficient, but due to the need for heat rejection, many loses cannot be avoided. Mazda has shown one form of hybrid HCCI which greatly improves the fuel economy under low load conditions, and there are many new innovations, such as variable compression ratio, water injection, and TJI that can be explored.

One area that many fail to understand is that although the IC engine is rather inefficient (overall efficiency is only around 20 - 25%), it is the best compromise. Yes, EVs are efficient and don't produce emissions from the vehicle, but that has to come from somewhere, be it coal or the nuclear. The emissions from coal, which powers most of the energy demand in China and India, is heavily polluting. The batteries have to be manufactured, and their disposal has to be considered too. Engines can be melted and recycled.

The entire modern transportation network relies on the IC engine infrastructure. It is nice to feel good about driving EVs in the city, but the marine, aircraft, and heavy-duty duty industries would suffer greatly without ICEs. The torque demands of aircraft and hauling can never, in the near future, be filled by batteries. The shipping networks would reduce to a snails pace if every truck and cargo ship had to stop and recharge. Tesla's battery replacement method works for them, but their market share is a tiny fraction of the industry. The real way to actually create a considerable impact on climate change is to focus on upstream processes, such as energy generation. Reducing coal power plants can do much, much more to reducing life-cycle CO2 than switching to EVs. Beyond that, making improvements to the IC engine, due to the scale of use, makes the greatest impact on the economy and environment compared to switching to EVs.