So let's start by saying that the FF16 team began forming in Heavensward into Stormblood. They began hiring and training new team members and the veterans of the team became "Supervisors" ie. they worked on FF16 but peeked their head over to FF14 to give advice or approve things.

Throughout Stormblood, the new team members were being trained and developing content - yet it's widely regarded as one of the best expansions content-wise (Eureka, Savage, Ultimate) not to mention the new ideas they tried in the Extreme trials.

And then you had Shadowbringers, which in my opinion was also a great expansion, again being developed by newer developers since many were working on FF16 by this point.

Then Endwalker came about and we had Covid. Everyone made a wild assumption that Endwalker's content was affected by FF16, despite that you could see from the trailer and original release date that FF16 was pretty much COMPLETE through most of Endwalker. Meaning almost all those team members working on FF16 didn't have much to do and would have had plenty of time for other projects, such as FF14. They only needed a small number to remain for the DLC from what I recall reading, since all the work on the core systems of the game were done ie. battle system, engine, etc.

If you did an actual measurement on the development, Endwalker had about as much content as other expansions. People didn't feel that was the case primarily because they were not interested in the content, not because there was less of it. Island Sanctuary, for example, clearly took substantial development effort similar to Ishgard Restoration, but a lot of people wouldn't have cared for it. Variant dungeons clearly took substantial development effort, but because you did the routes 12 times then that was it, it didn't seem like much - the issue was that it wasn't made into dynamic, replayable content. Criterion clearly took substantial development effort, but due to it being high-end content and people feeling it wasn't rewarding enough, a lot of people did not "count" it as content. They also made another Ocean Fishing map and some Crystalline Conflict maps - I doubt anyone noticed that, but that is a lot of development resources as well. They also revamped all the old MSQ dungeon battles and some solo duties, which was also development resources, but once again players didn't see this as content they cared about.

So you see, Endwalker had all this development effort going on. The problem was that many players did not care about what was developed, or didn't notice it. Where development was affected, I think it was much more due to the effects of Covid delaying asset creation and things like that, particularly around its earlier patches.

And Dawntrail genuinely has the most content of any expansion in the entire history of the game. We've had some of these things, but never all of it together in one expansion. We are getting everything this expansion that we've ever had in any prior expansion and more: 13 dungeons, 7 trials/extremes, 5 unreals, 12 normal/savage raids, 3 alliance raids, 2 ultimates, 1 chaotic, 2 field operations and their 2+ raids (not sure if we'll get something else), 1 deep dungeon, 1 challenging boss after beating DD, 3 variant/criterion/criterion savage, 4 cosmic exploration areas, a new limited job, (although nobody cares, new pvp maps and revamped ARR dungeons)

In regards to them developing themselves thin, I have watched their career recruitment page for years. They have been hiring battle developers for years. And it makes sense - they need them to develop what I listed above for Dawntrail. All the battle staff they've been hiring for years are culminating in all the raid content they've been developing in Dawntrail. Last I checked, they were still hiring them and even advertised it at the live letter. They do hire quest writers fairly often too, but it's important to mention this is probably for sidequests; they obviously are very selective about who works on the MSQ.

You asked if the graphics update has affected development, but I can say that throughout Endwalker they were hiring lots of graphics engineers in anticipation of the graphics update and have still been doing that. I imagine they hired loads by now. Obviously they will have set them to work upscaling assets and things like that. Given they've hired so many graphics engineers, it makes sense to get a few of them to upscale old games like Ivalice Chronicles.

(In case you don't believe me about them hiring, you can see it on archive.org of their recruitment page over the years)

In regards to the recent mention of cost, he actually meant development cost, not financial cost. It was another way of saying he just made the wrong decision and didn't plan a normal version of FT. I doubt they would be hiring so much if cost was the issue, and just so there's no confusion, these hires are specifically for FFXIV (and show its logo), or specifically reference "long-time 10 year MMORPG", and clearly make reference to CBU3 or its location.