@TensorBackhand
i'm about a similar level than you and for a long time i didn't make significant or huge improvements, despite taking coaching lessons.
I try to have a balanced game as well, attacking from both sides, i'm too old to take to rely only on FH as I used to when I was in my 20s.
I think i'm finally seeing some more results recently. Which is the consequence of many little - or not so little - things.
- improving takes time. You cannot build Rome in a day. When i took a new coach, just before Covid, what really changed is when instead of having the weekly 2h lesson at my usual sports center, which is crowded, i started going to the TT school where it was possible to work with a bucket of many balls, instead of 2-3, So in the same amount of time, i play 3x more balls = train 3x more.
- on top of that i soon started to do multiball. For nearly 2months, my coach wanted me to correct my basic shots. basically a reset of my basic technique. I was doing many things wrong, like sometimes a strange movement with my arm twisting strangely and the swing going up instead of forward etc...
if the basics aren't right then its difficult to improve beyond a certain level.
- after doing that, started to do basic footwork drills again and again. it develops the technique but also the muscles and stamina. then i get more muscle strength so gradually i can get lower on my feet, and move more quickly etc..
- all this would seem quite boring as i spent months doing very little game play during the coaching lessons. sometimes none at all, typically more like 15mns to 30mns on average per 2h session. but I I think I'm finally seeing the dividends now as it was a necessary step for the next part of the training program.
Whereas with the coach now, its more like 30mns only footwork or basics and the rest is gameplay / serve-receive etc..
- its been only 1 year (and a half ?) that i decided to work more seriously on my serve. spending 1h regularly just serving. and more recently some strong guys joined the team, and I have the opportunity to get their advice and play more quality balls, which means i must adapt and im getting used to it. very important also for receiving better.
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the more i train, the more i improve but even the more i can see my flaws and where im not good enough and should improve in priority. its endless. so you shouldn't think that there is nothing you can improve. you can improve anything. I think you have to choose what you really want to improve.
as for me, because of my lack of quality in both serve and receive, i was perhaps like you and only good in rallies but struggling on receive and 3rd ball. 3rd ball depends a lot on being able to have a good serve. if you serve is shit then the opponent can make difficult returns and has more options. so it makes attacking much more difficult.
then receive, its important to play with stronger players who have good serves.
the goal is at least to have 2 good set of serves: one for each lateral spin (for example pendulum + BH or pendulum + hook) which you can do with the same swing long short back / top / knuckle.. and then have at least 2 options against each type of serve.
basically in match you cannot improvise a new serve or new receive. you have to practice it a lot to be become strong in the first few shots of the point.
so i decided to work a lot more on serve/receive/ 3rd ball recently.
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as UpsideDownCarl says the better is that you post some videos.