My Japanese friends can't believe how long it takes to travel from Bangkok to Malaysia by train... "20 hours, it sounds like you are going around the world".
Unfortunately (or, perhaps, fortunately) there is no shinkansen in Thailand. No bullet train to Malaysia. On one hand, this is indeed a pain in the ass. Id love to shoot down there, spend my few days in Penang, and then shoot back.
On the other hand, there are benefits to slow travel. Slow travel feels more intentional. It provides more time for thinking and reflecting. Slow travel is more contemplative......
On my journey to Malaysia, Ill read a new book... stare out the window at the Thai landscape, chat with other passengers. Ill write in my journal. I make notes for article ideas.
And in this way Ill make a slight mental transformation... a small inner journey... to match my outer one.
For this purpose, slow travel seems superior to getting there quickly.