The Python is fine for mining - the key is to use one for just mining and only have mining gear. Especially for mining tritium in the middle of nowhere, which is about as low-risk an activity as you can do in the game. When I said ideally 8 collectors, that's what I use on my mining Python. The aim is to fill your hold quickly, how much you can actually collect in any one session isn't really important. I don't have a fuel scoop (I don't need it for making one or two jumps to a mining location and back) and I don't have a shield (nothing is going to shoot at me) which leaves plenty of room for cargo racks even with more collectors.Or it could be me that is terrible at mining - Just started doing it (and not liking it). Sounds like I need a bigger ship to fit more collector limpet controllers.
If you're new to mining completely then yeah, that's also going to be a factor and you do get more efficient with practice for sure but filling anything with just three collector limpets out is a drag, which probably won't be helping with giving you a negative impression of the activity.
End of the day though, a lot of people just can't stand it and you might be one of them, in which case stocking up at stations is probably your best option.