> "Most senors developers can leave and get another job with a 30-40% higher pay" and that "most current developers stay because of the flexible time and casual environment" is a very strong point.
One of the worst things a developer can do is to underperform on purpose because of thoughts like the above ("I could get a better job elsewhere, so I don't need to put in any effort here"). It leads to the worst possible outcome for everyone: low pay, bad performance, dissatisfaction on both sides. If you think you deserve better pay, ask for it or go find it elsewhere. If you don't, you were just looking for excuses to slack off.