This just patently false. Disney if anything overstaffs project to make sure things get done how they want it. At least in WDW and in the China parks. I don't have any personal experience in CA or France.
As to timely, I actually haven't seen too many Disney project (other than covid timeframe) with huge critical path schedule delays. However, what Disney doesn't care about is what outsiders perceive as timely. Construction projects are run per the construction schedule, they don't care when announcements were made, when hints were given out as to what might be built or D23 blue sky topics. A baseline schedule is created, accepted, and construction begins and is managed per that schedule.
Now I have seen openings be planned based around certain marketing strategies...which is what a business should do. It makes absolutely no sense to rush and open a new ride in 20 months, if opening it up in 3 months later due to seasonal demand, other maintenance issues, or a myriad of other factors makes the later opening more commercially viable. Its not a race to just get things done as quick as possible.