The reason flying represented only 2.5% of global emissions is because most people never do it. There's a small subset of people, mainly in the West, who do the vast majority of flying.
As this BBC article makes clear, a return flight from London to San Francisco represents half the emissions of the average London resident. If you fly a couple of return long haul trips a year, they'll emit the same as everything else you do for the rest of the year.
https://www.bbc.com/future/article/20200218-climate-change-h...
Looking at old aircraft will make the figures seem worse, but it's not like new aircraft are an order of magnitude more efficient.
The best case budget airlines (high seat density and high seat utilisation) today get about 2.27L/100km for each seat. The 737-300 was about 3.46L/100km - so about 65% of what it used to be. Better for sure, but not "we've fixed the problem" better. I'm not sure to what extent those figures take into account changing seat density and utilisation.
A far more common round trip London to Paris flight is ~6 gallons of fuel. So, someone doing that every weekend is still using 38% less fuel per year is using our 15,000 mile driver.
Flying only emits 2.5% of global CO2 because it’s surprisingly efficient and most people don’t travel ultra long distances frequently. LA to London takes a ~10 hour travel day each way making it unappealing to do frequently.
Your argument is also entirely generic. There is nothing that isn’t “irrelevant in comparison to industry and electrical generation”. Of note, “industry” can be split into arbitrary parts that would all fail your standard of significance. Meat production produces “only a fraction of CO2”. Residential heating, likewise, “produces a fraction of CO2”, and so do lighting, consumer goods, or the entire shipping industry.
Following your logic, nothing really matters, nor can anything be done.
It’s an activity that’s visible to everyone, it’s a personal choice (in the way that power generation usually isn’t), and a lot of air travel is a luxury and a convenience (again, more so than electricity).
Somehow the climate activists have decided to make a lot of noise about flying but it's mostly unfounded. They go as far as using very old models of planes in their calculations (e.g. a 737-400 model) and claiming that's the amount of CO2 per passenger of all air travel. While that model is out of use by the airline for at least 15 years already. It was designed in 1985.
So beware of the data and tricks like this when you're told flying is so bad for the environment.