Tricky situation...

If you create an wide opening the front of the case you may get better airflow for the CPU and the RAM, but you also compromize the negative pressure in the case that would otherwize draw air through the CD/DVD media drives.

They should have been designed differently. Yes.
They could still alter the design to reduce this problem. It would even make economic sense to do so as a result of the reduction in materials required. However, the restrictions that they have around "Class-1 Laser Products" in many countries requires that the casing be fully enclosed, by regulation. Hance, the dependency on the negative pressure airflow.

In your situation with 5 extractions fans you have plenty of extraction power, so the low pressure in the case should be ok, but if the opening you have created by removing one of the 5 1/4 inch blanks has allowed too much air intake, then the internal pressure will have dropped and you CD / DVD drives may not be cycling enough air.

You might consider fitting a grille to reduce the air flow slightly OR you could consider using an external CD drive case with its own fan which would separate the problem. There are also front plates with variable fan speed adjesters if you want to experiment and need greater control of your fans when gaming at high resolution and clocking them back when not playing.

This is definitely where the fluid and refridgeration CPU cooling systems reduce the dependency on air extraction from the case and I think this is one of their great selling points.

If you have a contained CPU / Graphics Card / Memory / HDD cooling kit and its cooling system or airflow path is independent of the general airflow through the case then you can run a minimal fan through the case to maintain the reduced air pressure in the case that the CD / DVD drives need. In the mean time your dedicated cooling system for your CPU or other device is looking after itself.

Otherwise, you can keep adding fans and opening airways and still compromise your media drive, so perhaps it would be better to provide the CD / DVD drive with its own air cooling path.

I had not really put much thought into that before as I had not needed to. But now that you raise it, it makes sense.

I have once created a custom dual-case machine where I separated the drives from the rest of the machine. I was going to make the external case into an array of swappable drives, but it got too expensive for my limited budget at the time so I scrapped it. It meant running an extra PSU for the HDDs but it worked while I tried it out.

Whilst Rack Units are a lot cheaper than they used to be, I found out just how much rack cabinets cost (just the bare bones) ... and almost fell off my chair

Besides, HDD capacity took off at that time and the need for extra drive bays is not such a problem anymore.

But perhaps the idea is still feasible for the home enthusiast that needs to separate the cooling paths of various devices.

Interesting.

How long can you make a SATA Raid cable ?
maybe I can dig this concept up again.
Anyone want to sponsor me ??? LOLOLOL