There are a lot of variables to someone's game. But there's a couple things we can look at. I use to be a "full roller" and what this means... your oil streak will be just left of the finger holes.... and then the streak clips your thumb hole. They claim full roller's can't generate enough striking power etc. If you're right handed... you leave a flat 10 pin... or sometimes even the 5 pin (no drive... no 5.) A full roller does have a lot of accuracy... usually very good spare shooters. But they have a hard time stringing strikes.
The proper oil streak on the ball (if you're right handed) is just left of the middle finger hole.... and left of the thumb hole. They call this a 3/4 roller. Most professional bowlers have this track. To acquire this track line... takes a lot of practice... and some are just naturally gifted. They claim a 3/4 roller can generate a lot of torque during the last 15 feet of the lane... another term for this is "back end."
Let's talk about the finger holes. Do you have a conventional grip? Semi finger grip? Or full finger tip grip? Do you use tips? Or no tips? Conventional grip is when you stick your fingers all the way to the 2nd knuckle. Semi is just below the 1st knuckle. And full finger tip is 1st knuckle. You can also do a full finger trip drilling pattern with... or without the grips. I've bowled with both.
Also, your thumb hole... do you go with a slug... or no slug. Some slugs are advanced now... with oval pitches etc. Slugs are used for a crisper consistent release. Some bowlers claim the material inside the bowling ball causes their thumb to stick. Again, a slug is made out of a different material... than what the bowling ball is made out of.
Then when you get your ball drilled.... you can actually change the pitches of the finger holes and thumb holes. Some bowlers want the ball out of their hand a split second sooner... you would slightly reverse the pitch of the finger holes to do this. Some bowlers wrists are weaker... and drop their ball a split second sooner... you can also change the pitch of the finger holes and it would help a bowler hang onto the ball.
Not trying to confuse you... just giving you the simple fundamentals of what pros talk about etc. There are some lucky bowlers who run into a ball driller... and they know just what you need from examining you for 15 minutes. Some ball drillers are gifted. I've gone through numerous ball drillers... I never found the lucky one for myself. It's all in who you know.
I actually took 1.5 years off of bowling. Stopped at 18. Started again at 19.5 to 20. Roughly. My friend was at the bowling alley and he goes don't you miss the game? I said... of course... I do. He said throw my bowling ball. We have 2 different hand patterns... and 2 different drilling axis points. I said oh the hell with it... I'll throw it. I had to stretch my hand. It was weird... because it caused me to drop the ball much earlier during my release point... causing the ball to get in full rotation quicker... and however his ball was drilled... it exploded the pins. I think I bowled a 242.... I was like in shock. He said you want the ball? It's yours. Now get back into bowling.
I had a couple of ball drillers copy the pitch of both finger holes... copy the pitch of the thumb hole. They drilled exactly to the replica of the original ball. Oddly enough... I purchased 2 new bowling balls... with identical specs. Both bowling balls didn't feel perfect on my hand like my friend's bowling ball. I even got into an argument with the ball driller... we almost started swinging it got so hot
I was like dude... you can't even copy a fukking bowling ball... and you claim it's perfect. Whatever.
So as you can clearly see... every bowling ball driller is different.
Another thing you can do on your own... set up a camera... or use your phone.... take a look at your back swing and release point. Record a few shots... play em back and see if it's to your liking. You'd be amazed at how some bowler's look like on camera... back swing.. follow through etc. It's always good to check yourself out.
There's a very good chance the core is cracked. Just pour water in the finger holes... if you can see the liquid rising in your thumb hole... your core is cracked. You can just dump out the water.... if the core isn't cracked... the water won't damage your bowling ball.
What happens when your core is cracked? You'll leave a lot of 10 pins if you're right handed.... 7 pins if you're left handed. Sometimes you can actually see the ball ricochet off the head pin... like it had no drive at all... and you know you released it well etc. The ball just won't have that drive that you're use to seeing. Basically the ball is deflecting... has no driving power... because the core is damaged.