Not revenge as much as financial motives. He wants less oversight on his business activities so he can make more money and be involved in fewer lawsuits and regulatory actions. There seems to be a broader motive to degrade the US and cause chaos and hardship, which I assume is other Republicans and influences like Putin. Some are probably favors to other interests - for instance, my guess about decreasing park rangers is probably to degrade parks and decrease attendance so they can justify drilling for oil or mining in national parks. The amount of money saved by slashing federal employment is trivial in terms of the budget, so it certainly isn't that. One thing is that before the election they said they were going to specifically make sure that agencies were staffed with Trump loyalists at every level, so I'd bet when you hear there were cuts at the FDA and the staff said they seemed random, everyone who was fired voted for Democrats, had Democrat supporting social media activity, and so forth.