Sure this all normal. I am a beginner at Judo and Jujutsu, so, I won't pretend to be an expert, but, it sounds normal to me. If you have been doing Judo for a while (like 2 years or more) there's a bit of a problem. But, beginners, sure, it's going to be hard. Judo throws are somewhat easy to learn. But, perfecting them (the timing, strength, power, kuzushi, etc.) takes a lifetime to master. So, just because you know are doing a throw in general there are a lot of smaller parts that make up a great throw. You are probably missing all of those smaller pieces and just have the bigger piece (something that resembles the throw you are trying). It's always going be hard to throw a heavier person no matter if you are a beginner or black belt. If someone is your size or lighter, sure, they are easy to throw. It's just that common sense you deal with something heavy it's always harder to move. A car will be harder to move than a bicycle. So, "Judo Magic," won't produce the magical throws who can also throw everybody effortlessly. It will always be harder worker for a bigger guy. I think you just need more time. I'm sure there are many Judoka who can throw bigger opponets. It is all in the details. I mean I'm right here, trying to throw people myself on a weekly basis. I have the idea of about half a dozen throws in my arsenal. But, I don't have my timing, kuzushi, strenght, power, technical mastery, or it down. With lighter people I can just muscle my way through it and plant them on the ground. But, here is the other part of your question, if they are skilled and resist, they are harder too. But, it's the same thing as the bigger guy, a lighweight skilled resister just takes all those smaller parts of mastery too. It takes time. I see all the potential of the many Judo throws, takedowns, and sweeps. There is more than one way to take anybody down too. Judo has many weapons to choose from as you go up the ranks too.