The statement was the new system is an upgrade on the old system, which it is because its the old system with options to choose from.
1)Gear being rare with no titanforging or warforging increases the odds of a single completely random high ilvl piece being an upgrade which actually devalues the potency of being able to choose a piece. (but its still better to have choices obviously)
2)We clearly have very different scales for what "middle of the road" means. If you are at the point where you have optimized M+/heroic raid gear which is the usual perpetrator for being able to out value a random mythic quality piece your gearing process is near done, not near the middle. And finishing your gearing, to be perfect, has always been tough. So yes people who spend more time doing more content will be able to use their chest to optimize end game gearing faster this isnt a problem because you are talking about average variable ilvls of 1-2 and I've never seen some pug lead for regular content deny someone cause they have slightly better itemized gear.
3) I'm sorry but I'm not 100% sure on your point here but ill give it my best shot. You think because raids have limited gear drops compared to the whole of the M+ pool that the raiders get an advantage by picking from more of the raid pieces which are at the same ilvl as the M+ pieces? If my understanding of the system is right you will only see 1 mythic raid piece to choose from until you are killing 7 mythic bosses per week. Usually the OP raid items are trinkets. Getting a properly itemized raid piece is the same gambling shit show as M+ pieces. Nya for example only had 1 piece with BiS itemization for my monk(not counting azerite). So I guess the concern here is raiders are gonna get raid trinkets faster? potentially at the loss of getting well itemized armor slots sooner. On top of that, like you said raids have more limited loot pools so getting trinkets from raid is already pretty easy via targeting with coins. The only heavy acceleration of trinket acquisition will be from drops that come later in the raid that are not being killed in your raids first couple of clears.
I raid top 100 US and we will certainly not be requiring anything of the sort. The % of our players that will do 15 M+ per week will probably be sub 30%(estimate of course). The number might be higher for the first 1-2 weeks but that is more likely due to just wanting the higher ilvl base drops with the chest rewards being a secondary reason.