It does depend on the quality of hour building, what you do in those hours flying a C152. You should be doing some flights that are constructive and useful, well planned, and not just flying donuts in the sky.
I believe it's excellent experience to fly light aircraft for your skills, specially to build up confidence for decision making, threat and error management, situational awareness, and build up confidence to take decisions on your own, which will give you invaluable experience for you later aviation career. As you only have yourself to rely on, and it will give you the ability to learn not only about aviation, but also your own ability and limitations. You will take all decisions your self regarding fuel, weight/balance, navigation, weather, radio ATC, flying to different airports, different locations, terrain, approaches etc., which are all skills you need to improve from the time you take your PPL until you become a skilled commercial pilot.
FI hours are in my opinion not equally beneficial, as you are not flying yourself, and generally you are doing a "fixed" program of exercises, so these hours although they count as PIC time, is mostly demonstrating a handling skill, and observing the student practicing this. It adds hours in the log book, and I don't disagree that it can be a good experience to have, you should have some own "real life" experience from flying before starting to instruct others.