I must confess that what you describe is counter-intuitive. Playing at the tip, requires more force than playing at the frog because there is lever-arm that you must overcome. To have power at the tip, you need to use more rotational force than at the frog, where you can rely on the weight of your arm to provide the necessary pressure.
It sounds like you are way too high with respect to your cello. I can think of a few possible explanations:
1. Your arms are way too high, which can cause shoulder problems later.
2. Perhaps you are quite tall and you tower over your instrument. In this case you need to put a stack of books or a thick cushion on your chair.
3. You are holding your cello too low and you need to pull your endpin out some more. I hold my cello such that it touches a couple of inches above the bottom of my sternum.
Different regions of the bow have their strengths and weaknesses. If you are playing a passage that has a lot of rapid string crossings or uses a variety of lengths of bows, playing a little more towards upper half is better. You don't have as much power though. The lower half has the strength, but it's harder to maintain control in complicated bowing passages. But you should have good control in all regions of the bow. It's just that some regions are a little better.
Regarding your point about instrument quality: Yes, it would be nice to own the Du Pre Strad like Lynn Harrell. But this is not realistic. You can learn a lot even playing on a poor instrument. There will come a time when your technique reaches a point where the instrument holds you back. But unless you've got a real beater, don't let this become an excuse for not learning. We all have to make the best of what we've got.
You should take your instrument to a shop to verify that it is set up as best as it can. Make sure the strings aren't too high or too low. Make sure that the sound post is in the optimal position, etc.
Click on the jet to return to the second page of cello tips.