The Einstein Nobel situation was very political. More and more physicists each year thought that Einstein should get it for special relativity, and later for that and/or general relativity.
However, there were a few physicists who thought specially relativity was bunk, and that included some who were very influential, such as 1905 Nobel winner Phillip Lenard. Until experimental proof of relativity was found, they had no trouble keeping the prize away from Einstein.
By 1919, when there was sufficient proof of general relativity that the "it's not been proved" excuse no longer worked, Germany had lost World War I, and a lot of people were looking for excuses to explain that loss, and Jews were a good target. Especially pacifist Jewish scientists like Einstein who had refused to turn their science toward the war effort. The prominent nationalist scientists, like Lenard, saw people like Einstein as practically traitors. They labeled relativity "Jewish Physics", as opposed to correct, "German Physics", and ascribed evil intent to those trying to mislead Germany with their fake Jewish physics. (Lenard went on the become "Chief of Aryan Physics" under the Nazis).
In 1921, the Prize committee did not find any of the nominees that year worthy, and considered not awarding the prize that year. This would make the already ridiculous situation with Einstein even worse--it's one thing to not give Einstein the prize because you give it to someone else. That at least makes some sense--at worst you might be seen as misjudging the importance of the winning work. But to say there is nothing worthy out there at all, when Einstein does not have even one of the arguably 3 he deserves? Absurd!
But giving the prize for relativity would piss off a lot of nationalist and/or antisemitic Germans, both among German scientists and German politicians. In the political climate of Germany at the time, this was not a good thing to do. Germany was still one of the most, if not the most important science countries in the world. Scientists do have to live in the real world, so there was reluctance.
Someone suggested that they give it to Einstein, but make it clear that they are not endorsing relativity, so he got the 1921 prize, "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect" with a note that this was "without taking into account the value that will be accorded your relativity and gravitation theories after these are confirmed in the future".
Given all that, I don't think you can infer that the Nobel committee giving him the prize for the photoelectric effect necessarily means they thought that it was his top accomplishment.