Firstly, the article in the OP is admitting there are issues with maintenance on the ARL.
Secondly, the accident on the KLIA Ekpress was minor and did not result in the shutdown of the service.
Thirdly, you are way wrong about the speeds of both systems. The ARL operating speed is 120kmh while the KLIA Ekpress is a proper high speed rail with operating speed of 160kmh and top speed of 200kmh.
Finally, KL is a much nicer and more picturesque city than Bangkok. I prefer Bangkok, because I love it having lived there 34 years, but comparing the two you have to be objective.
I didn't even mention the many incidents with the ARL including the frequent power outages, the death of a woman on the tracks, mechanical problems etc.
As a frequent user of both services, the KLIA Ekpress service is far superior. No question.