That logic doesn't work because then you'd have to give automatic berths to the champions of Montenegro, Kazakhstan, Slovenia, etc.
You might reply "well then, only give the automatic champions births to the strongest UEFA countries." To which I'd reply by pointing out that this is exactly what happens!
It's all based on the performance of a country's teams in Europe in the previous few years. Scottish teams just haven't done well enough to keep an automatic birth.
I can point to one example I know - the champions of Russia went straight into the group stage this year after previously having to qualify. And Russia has a qualifying spot for the number 2 team for only the 2nd time this year.
I'm sure you know how this works... so why would you possibly think Celtic deserves an automatic birth?