I agree it would be "out of place", and I agree that position matters, and also that it is unlikely for the station to debut or remain in the 600's.
Channel position remains important ... even in the age of DVRs and receivers that find programs for customers. Similar channels together in the guide is expected - and when a channel is "out of place" it is noticed (and someone usually starts a thread saying "why is channel X in position Y" to complain about it).
If position didn't matter DirecTV and DISH would never move channels. They would be listed in the order added. They are not.
I do not expect FXX to stay at 619 on DirecTV. It would be out of place.
BTW: DISH currently has Fox Soccer Channel on 390 along with other special sports channels (FSC+ on 391, BeIN on 392, away from the ESPN channels in the 140s). DISH has 137 available next to 136 FX and 138 TNT/139 TBS so FXX (FX for generation X) could be moved there.
My position is not that position does not matter; it is that it matters much less than ever before. And I do not accept either of your arguments to the contrary. Some yahoo with too much time on their hands and nothing else to complain about deciding to spend their afternoon complaining on Twitter is not a cogent argument for how important position is, and speaking as a long-time industry insider with direct knowledge of why certain decisions are made, neither is your complete guess regarding why channels are slotted where they might be by DBS.
That is like saying the sky is blue because it always has been and no one's complained about it.