Bit of a tangent: Around here, and likely in many other places that were developed before double-digit YDS grades were a thing, 5.9+ is a specific and notorious grade, that is usually closer to 5.11 than 5.9.
Does that explain why many outdoors top-rope and lead climbing routes in the US feel about two grades harder than equivalently graded indoor routes? Specifically east-coast but I've heard the same applies nationally.
I think that’s just gyms grading soft to be honest.
Gyms are just a different thing. There a few places where gym grades translate well onto real rock, but they are few and far between, and nowhere with mostly trad routes will translate. Smith Rock for instance probably translates fine. Yosemite does not.
the hell kind of gym are you at that Smith Rock grades feel comparable? that place is sandbagged as hell.
A moonboard!
gyms are typically softer to give their clientele a feeling of progress. this makes people feel better and want to come back. if you're stuck at v3 for several months you'd be more likely to give up telling yourself you're not cut out for climbing... at least that's my(and many others') theory behind soft gyms
outdoor climbing is also usually a completely different style. I've found that often outdoor routes have way more focus on leg work. and that find a good hand hold is way more determined by how well you can read the route rather than how good the holds are in practise. Also people making the routes outside are often way better climbers so they often don't have a good pulse on grading the lower grades. Plus adjusting a routes grade based on feedback isn't really a thing because lowering the grade of a route after it has been set is quite the insult to the credibility of the person who made the route.