A part time red teamer is just a pen tester. That's not what a red team does, and adequate threat emulation isn't someone who flies in for two weeks does somethings that you can only accomplish in two weeks, then fly out to the next company to do the same things. You actually need to dig deep and research a companies individual weaknesses and that takes time. Threat actors have that kind of time to sit and observe and probe, a part time noisy pen test isn't going to get you more than the basics.
Also a blue team has to be right all the time, the attacker only has to get things right once. That's why you constantly test your assumptions with a red team and give blue someone to "train" with and improve with that isn't an actual threat actor. You don't want the first time you fight to be in the ring, you need to spar.
A lot of pen testing consultancies brand themselves as red teams, but a lot of them are just rebranding pen testing services to the ignorant.