You've never done programing in your life, have you? The only reason they would have to worry about something like that is if they had interdependencies of abilities between champions or messed with the base code. In other words spaghetti code or someone messed up in changing how a stun works for all champions. In the first case, it's bad programming (and it's worth noting they've done multiple passes through their programs to rewrite their spaghetti code over the past few years; most recently with Mord). Second case is unfortunate, and it's something we saw this recent patch. They rewrote a lot of base game functions and a lot of things went wrong from it.
Normally such things would be understandable, but with the scale of it this patch, that tells us they didn't do proper QA of it. As for regular bugs sitting in the game for a long time, most of that is small-scale spaghetti code probably. In fact all the champion bugs I keep listed on my computer would fall under that. So, again, normally it would be understandable. It takes a lot of time to sort through that. What isn't understandable is why it's been passed over on priority for so long when some of them are high impact bugs. Some of these bugs have a high impact for gameplay, feel of the champ, or both with high replication rates and they've been around for YEARS.
They haven't been doing big changes this year. Almost all their changes are low in time/resources that they've done so far this year (at least in terms of programming). So they should have had spare resources to put towards bug fixing. Not asking/expecting a lot, but over the course of a year three extra people could have done a lot to reduce the bugs in the game, especially the higher impact/standing ones. So where are these resources? What are they being used for that's so important? To me it looks like it's been monetizable items and TFT. Both of which don't completely cover the extra resources they should have.
Again, 3 people isn't a lot. But they should have a bit more than that assuming they haven't downsized and based off what they've been able to undertake in years past. In actuality they've been hiring this year, so they should have even more than I expect. That brings us back to the point. What do they have these people working on? They've essentially pulled resources from balance with some going to income, and some going to TFT; the rest is either working on something to be revealed, or they've horribly mismanaged their resources somewhere.
TLDR: The program/amount of code isn't an excuse, coding is not nearly as complicated and code is not as nearly intertwined as you think. And I'm annoyed because they're pulling resources from balance and not putting enough back into bug fixes and champion vgus/releases (of which I currently care about bug fixes more).