A variety of ideas and theories have been shared here. I'll let you know what I think. Have done 1000+ hrs instructing in C172.
1) Landings are the hardest part to teach, because it comes down to "feel" and nothing that can be taught in words. Learning is a result of experience. You need to practice (a lot). Some people get it right the first time, some people take many sessions before they get the hang of it. They are all very fine pilots today.
2) Unless your instructor lacks patience and generally annoys you, I wouldn't be too quick to change instructor. Certainly it could be wise to fly with another one, once or twice, to get some new inputs. But it would be unfair to get rid of your instructor just because you need more practice to get the right "feel".
3) Hot days, as you describe, tend to upset the natural behavior of the aircraft. Even I can get pissed at myself when I sail through my planned touchdown point with several hundred feet. I am floating on a bubble of rising air, just waiting for the sink through to come. Eventually it will. But if too focused on your touchdown point you may force it down prematurely, with still too much lift, resulting in 3-pointers. Try an early morning or late evening flight, with less thermals?
4) To avoid pilot induced oscillations, once you've started the flare don't move the yoke forward. If your descent rate stops, hold the yoke, let the speed bleed off and once descending again apply more back pressure. Only if you get critically low on airspeed, move yoke forward and add power to prevent a quick sink.
5) Don't worry about the touchdown point until you've gotten the "feel" for the flare, as long as you've got runway remaining. That can be sorted out later.
Btw, C172 is approved for spins in utility category, at least the re-starts. Safe and legal. They are even fun to do!