7 ft and 9 ft side by side....7 ft is like half the size.....you can't use your toes to pop up on a 7ft and has a third less volume. You will not outgrow a longboard....IMO one should stay in everyone's quiver....last time I rode that longboard it was 1.5OH (9-10 ft faces)....you WON'T plateau or outgrow it.....
You also won't learn if you can't catch a wave.....personal experience was that on a longboard I went from 2-5 waves in a two hour sash, sometimes none to 25+ waves a sesh....then I went to a 7'6" and was back to 2-5, sometimes none. The things you need to learn now are not necessarily riding the wave as much as reading waves, learning where to be, timing while catching, streamlining and making your pop up faster without looking down while looking down the wave, how to be clever getting out back even on a big board, and paddle fitness....always paddle fitness....spend the needed time on a bigger board (200hours give or take) working on these things, learn how to get up and get down the line left or right ALL the time in good conditions, then again in onshore, windy or otherwise crap conditions....build your posture while paddling, refine the paddling technique you have.....all of this will serve as a foundation and is MUCH easier to build that on a bigger board without giving away anything.
When I was starting out I was convinced as well that what was holding me up was that my board was too big to get out back through waves.....if I could just get a board small enough to get out back I said to myself.....long story short, I got a smaller board and duck dived my way out back only to not catch a single wave in two weeks.....yes two weeks.....I went back to my bigger board and found that after I put the time in doing the things that I said above, after I got good at catching and going down the line on waves waist high my paddling had improved.....and my ocean reading had improved....I figured out how to time my way out back between waves and sets.....was able to paddle out and keep my hair dry on days I previously couldn't even get out back.
I was out the other day and a
surf instructor on an 8 ft foamie hit the lip going nearly vertical.......you need to get off the foamie and on a board with real fins....but ATM it is not the board holding you back. Go too small too fast and it will be the board holding you back.