I have lots and lots of problems with the OP's post.

First, based on my experience, and provided you are familiar with the layout of BKK, it would never take an average person 25 minutes to get from a domestic gate to the furthest international gate, and is nowhere near 2 km. Provided you use the travelators, it should take less than 5 minutes to get to the domestic to international 'check point'. From there, maybe 8 minutes to get to the opposite side of the D concourse where the E/F/G concourse meet. From there just a couple minutes to E2. Total maybe 15 minutes. That is provided you used the Level 2 travelators to traverse the D concourse. If you traversed it through the duty free shops on level 4, then it would take longer, maybe 20 minutes. If you walk rather slowly, then I can see it taking 25 minutes. Regardless, this has nothing to do with TG. It is an issue with BKK, but I don't know of any major airports the size of BKK where the transfer time is significantly less, and many where the transfer time is significantly more. So BKK IMHO is much better than the average airport.

When I last transited domestic to international at BKK just a month ago, there was no real security checkpoint. Just a guard to verify that everyone had their "CIQ" stickers on. They didn't even check my passport and there was no x-raying of luggage. I didn't even stop as I passed the guard, so unless something has changed, I don't see why the need to even mention that. There is a normal security checkpoint at the concourse entrance to the gates, but this sort of thing is standard in Asia. You always have at least one security checkpoint even for transit passengers. Nothing specific to TG and nothing specific to BKK.

As already stated, the E concourse ROP lounge is right next to gate E2. The lounge should not have been an issue.

The OP stated the flight from HKT to BKK was the worst of any flight ever. Ok, but why? Simply stating it was the worst without going into any detail doesn't help any of us. If you're going to complain about something, at least tell us what it is you're complaining about.

The same for the flight from BKK to ICN. At least describe why it was so bad.

I think the problems experienced at BKK were likely due to the OP's unfamiliarity with the airport. The same sort of thing could happen at almost any airport in the world. If you're not familiar with it, you can expect it to take longer to get from one point to another and if not familiar with all the lounge options, you may miss out on which is most convenient for you. If you didn't take the time to research the airport first, just chalk it up to experience. I don't personally see the need to complain much especially if you're an FTer but didn't bother first to read up about the airport on FT.

For the TG problems, please do explain in more detail what your issues were and then see what the response is from fellow FTers. Not trying to say you don't have valid complaints, just we need more info if we're to agree with you or offer suggestions for others in how to avoid whatever problems you may have had.