Of course you are. And you also know 'engineers' who bought their papers. But those 4 years were enough to reveal your aptitude -- not to shove more than cursory knowledge into you -- show your aptitude: being on the job has turned you into the professional you are now.
No. You are considered a "professional" as soon as you enter the job.
Yes, I know that. But that is superficial, at best. No one can be 'developed' in 4 years -- or in 8 years of school. In Canada, a new engineer is 'mentored' for a period of time. I don't think the system is as productive as it could be, but it is in the right direction. Many young engineering students do their studies as 'co-op', whereby they intersperse classroom study with job placings. It prolongs the time that they are officially students, but it greatly increases their scope and on-the-job training.