In WoW, you can only boost one character with a boost and not to max level though, while the story skip counts for all classes on this character in FFXIV. With SE not really encouraging making alts ad keeping this game heavily story-focused it's understandable that you'd need to pay more for the story skip. And there's a MUCH larger focus on endgame in WoW.

Also, I don't quite get the problem. Shadowbringers is still months] away.
You said that he returned from ARR content. You get to 50 fairly fast, even faster if you play as tank or healer and have short dungeons queues. If the queue is really long and he needs to a dungeon to progress with the MSQ, PF is always an option if no friends are online to help him. Had plenty of people help me out during my ARR Relic quest with the 50s dungeons, because the DF was empty af and I had 40min+ queue times as a healer but takes like 4-6min for a 70.
The ARR to HW transition is a bit tiresome and can take several evenings. But if reaching 70 & finishing MSQ as fast as possible without buying a story skip is his focus, then he can always skip all the cutscenes, already saving him tons of time and enjoy it later via new game+. Even if he can't play that much, he could probably get from 1 to 70 in time without excessive cut scene skipping.

And of course catching up takes a bit of time. So starting a few month before a new expansion obviously means, you've already missed most content when it was relevant but he's a far cry from "not reaching endgame in time". And even if he reaches max level shortly AFTER Shadowbringers hits, unless he is in a rush for server firsts, it won't matter. Queue times are a nightmare if you are ahead of the curb with the MSQ, nothing I would recommend.
And wether he does old max level content synced now or later doesn't make much of a difference. Sure, some classes will get reworked, but he's already long past the point of "playing it as it once was".

But honestly... with the heavy focus on story, world building etc, everything from 1 to 70 is what he paid for.
I fail to see why someone would rush through what is and always has been one of the major selling points for a game (on his first char no less) to get to endgame a few month before a new expansion hits.
The reason for implementing new game+ was largely the players wanted to replay the MSQ because they enjoyed it. Because they'd rather spent more time leveling a new class through MSQ again then spamming PotD/HoH. But he thinks of it as slog and a waste of time.
I can't help but think that maybe he should reconsider why he is playing FFXIV of all things when it was never a secret where the focus lies.