The key points / counterarguments I seem to take from Vidu's standpoint is that, and from others:

1. Difficulty is demanded by players, and it is only logical that SE designs raids to be difficult, to both entertain and challenge these dedicated players.
2. The urgency to gain rewards is not actually that high as even purely via tokens or low efficiency raiding, you'll be well geared before the next tier of content hits.
3. Any changes will substantially alter the nature / form of the content, not to mention will be difficult to code / implement. Current doability does not warrant dismissal of the viability of current content as a natural and balanced form of progression in the game.
4. Other people point out there are no existing examples of such a system in similar game design, probably for good reason.
5. Other people point out be careful what you wish for: Systems were not meant to be slotted into each other, or modified to address singular problems.
6. The actual efficiency of the key idea under inspection (no-death / wipe practice mode) is doubted, or questioned to not target actual problem points.

I think some of those would be quite difficult to discuss. Not to mention SE seems to have their own raid design philosophy already, and what a raid "should be". How the game should provide its entertainment efficiently, etc.

However my own motive for thinking up this idea, was mainly for the following points:
1. Having to re-run all prior mechanics before seeing later mechanics is highly inefficient, especially when factoring in the inconsistency and inefficiency of PF practice, with people leaving, failing randomly, new groups and tactics and positions every group.
2. Not having to worry about death will lessen mental pressure on players. This is a good thing. They will learn better when happy.
3. Being able to run a whole fight coherently from start to finish, players can focus on the actual mechanics, observing raid, memorize timing and rotations, experimenting with raid cds. Try out new tactics and strats.
4. A successful run does not mean the end of a night of raiding. When I practice music I don't stop when I happen to do a piece perfectly. You can also run it again and again until you can do it in your sleep. At any rate, being a "successful" run by definition is much more satisfying than wiping in PF more times in 1 week than you've done for the whole expansion.
5. If the general efficiency of the whole playerbase increases, SE can experiment with new forms of content, new content scheduling, new design philosophy. Utilizing this system and data from it to create even more creativity and content. It's a compounding effect. It's all about creating "systems", with better PF tools, etc.
5. Having a leisure mode allows helping out others, such as FC members, practice before they "go out into the wild" and find their own clear groups.