It's not even just that it is "thought" about. It is an objectively true statement when it comes to aircraft technology. I won't go over what the general sentiment, there is no objective way we can determine how people generally thought.

We have polls today for that, but back then there was no polls about this so there is no true answer to that question. I apologize but maybe someone else with a better understanding and access to relevant research can answer that.

Japan was significantly behind in aircraft design/construction from the 1920s all the way into the early 1930s.

Here is the Army's situation when it came to aircraft technology. During the time, the bidding process was that the Military would give out several requirements for a plane (Although, really anything that was to be manufactured.) to companies. And they would make prototypes to compete.

Japanese companies was never able to meet the Army's requirement for the planes designs since the early days of aviation technology.

I'll jump directly into the 1920s as per your question here. In early 1920s, the Army adopted the NiD 29, licensed manufactured by Nakajima Aircraft. The Japanese aviation companies were still not able to compete with foreign designers.

The NiD 29 was used until in 1927 when the Army ordered another prototype, this time the Japanese companies, Nakajima, Kawasaki, Mitsubishi, Ishigawajima, all hired their own foreign adviser and expert designers to compete.

They were finally starting to have some practical knowledge on building, but still needed theoretical experiences.

But during the 1929 test trails, ALL the prototype planes from all the companies experience catastrophic failures. From basic design problems to manufacture issues.

In the end, the Army choose Nakajima's plane which had "minor" problems compared to others. (It rapidly disassembled while diving...) The Army had Nakajima improved their plane and finally adopted it. The plane still had the problem of going into a spin while flying horizontally.

One thing worth mentioning is that Kawasaki's competition plane, while spectacularly had engine failures during the trail was actually the best paper spec wise. But Japanese copy of the BMW engine it used was plagued with reliability problems. Later on, not satisfied by Nakajima's improved plane, the Army actually asked Kawasaki to improve on theirs, and later adopted their version one year later.

As you can see, the Japanese aviation companies although learning, still didn't had it down. Both quality control wise and design wise.

After this failed design competition, the Army went back to license manufacturing foreign planes for a couple years again. And licensed manufactured their bombers during this time mostly.

In 1934, already in the 30s the Army ordered another fighter to be designed after being dissatisfied by the German designer Richard Vogt's design (He designed a bunch of funny weapons for the Nazi's later on, none of them were adopted).

This time they finally got it right, with a bi-plane, keep in mind this is during an era that all new planes were designed with single low wing much like the ones we later see during WW2. The plane was good, no big issue anymore and the reliability wasn't exceptionally bad. It was acceptable, but it was behind technologically in the World.

Finally, in the 1937, a new plane was adopted. The Ki-27 Type 97 Fighter. This time, it's a low wing monoplane, with a good engine. It had amazing dog fight ability and turn rate, but it still lacked speed, and armament was also significantly underpowered (2 .30 cal machineguns mounted on the cowling). It also didn't had retractable gear.

When you compare it to other contemporary plane designs during the era, like the Bf 109 and Spitfires you will understand how significantly behind the Japanese was in their plane designs,

Look at the spec lists for the Spitfire, Hurricane, Bf109 and compare to the Ki27, and you'd see how bad it was.

But, having said all that, the Japanese learned a lot through their trial and error and fast too.

In 1938, immediately the next year after Ki-27 was adopted. The Type one fighter, Ki-43, Hayabusa was adopted. The Army after seeing the performance of the new Western fighters was worried about their plane being worse than the westerners (They were right too.)

The fighter was arguably the best effort Nakajima could've put in, both design wise and manufacturing wise.

But the plane, was still significantly behind the westerners. It had several problems. One, the propeller design was still 2 pronged propeller. Two, the armament was still just 2 7.7mm MG in the cowl. Three, the engine was still significantly underpowered than the western fighters. (It had 950 hp, while most other contemporary western fighters had over 1000 hp).

However, even in this condition, the Japanese learned fast. In 1940, the A6M Zero was adopted by the Navy. (Which, had been using the A5M Type 96 for years now.)

Mitsubishi, with the experienced learned by Nakajima and their struggled designs, finally put out what was soon to be one of Mitsubishi's most famous design in the world.

The story of Zero's design is a long one so I'll be skipping and, and it also is at the end of the 30s as well.

In the end, I can tell you it's definitely possible (Almost guaranteed really) for a Japanese aircraft engineer to think Japan was behind on aircraft technology when compared to the westerners in the 20s and (early and mid) 30s.