So I would consider this a separate, but related question.
There's "am I pressure testing my skills?"
and there's
"can I accurately gauge the difficulty of my pressure testing relative to a real-world encounter?"
This second question still exists even if everyone in your gym is going 100% every round. If you don't have the experience to tell that an upper belt is only giving you 20% effort, then you probably don't have the experience to know how good your sparring partners are relative to a real-world attacker on the street.
Perhaps you think your sparring partners are a bunch of hardcore badasses, but they actually suck. This can make you misjudge your own abilities just as much as thinking your coach is going 100% when he's only going 10%.
In fact, it's more of a risk. If your coach is only going 10% with you, then he will up the intensity as you progress and you'll realize your mistake. If you train at a gym where your coach and sparring partners just aren't very good, then you may not ever realize it unless you get out from your bubble and test your skills against someone tougher.
This is why I strongly recommend both cross-training and welcoming guests from different backgrounds to your gym.
I make no claims to being an especially tough guy or a super-skilled fighter. But I do think that I have a reasonably accurate idea of my own abilities and limitations. This comes from decades of training and sparring with:
- Boxers (professional fighters, amateur fighters, and hobbyists)
- Muay Thai practitioners (professional fighters, amateur fighters, and hobbyists)
- MMA practitioners (professional fighters, amateur fighters, and hobbyists)
- High school wrestlers
- Collegiate wrestlers
- BJJ practitioners (white to black belt, casual hobbyists to professional competitors)
- TKD and Karate practitioners (various styles and levels)
- Kung Fu practitioners (various styles and levels)
- Judo black belts
- Representatives of many other styles (ninjutsu, Aikido, Kali, Sumo, Sambo, HEMA, etc)
- Strong-man competitors
- Powerlifters
- Cops
- Soldiers
- Bouncers
- Untrained individuals (with various degrees of experience in street violence and natural talent)
- Young guys, old guys, men, women, little guys, big guys, really big guys
... and I have a small amount of experience with real violence outside the training hall.
Honestly, I think this exposure to different types of training partners and opponents and sparring styles does a lot more for being able to judge one's level of ability than just having your regular training partners go 100% in sparring. You might find that you are able to deal with a skilled technician within your style but fall apart when faced with someone 4x stronger. (Or vice-versa). You might handle strikers well, but struggle with grapplers. (Or vice-versa). You might out-point a partner in light sparring, but psychologically crumble in harder sparring when that same partner doesn't mind getting hit and keeps coming forward.
But all this takes time to experience. So to begin with, the best bet is to just find an instructor who will structure opportunities to try your techniques in live environments where you have the opportunity to fail and learn from those failures.