How to disarm bomb on the attacking side, DICE???

If anything, it's bad luck, not a bug. Game connects players to whichever team has lower playercount. Also, there were multiple ways to get on a team that can arm the objective...

1) Play Frontlines. That mode doesn't have attacking and defending side - either side can arm the objective if it's good enough to push enemies back to their base. You don't need to be on a particular team. I actually got my defuse there.

2) If you are put on attack on Grand Ops, just stay on the server after the match - vast majority of players is moved from attack to defense (and vice versa) when new match starts. The only exception would be players moved between matches to balance teams... and there isn't a particularly high number of those.

So, overall, no, there was no laziness here. Getting on a team that could defuse an objective was very much doable and simple. Putting aside that that task was not necessary to unlock the Archer either.

(also, feedback is more suited for https://forums.battlefield.com - please use the bug report section of AHQ for actual bugs)

I think if the game was well optimized, it would connect to those servers that have the spots on the right team, not just any team. Or do only I think so?

I certainly disagree. Game's priority is and always should be to keep the number of players on both sides as close to even as possible. I have not played a single FPS that would place you on a particular team based on asignments you have... because that's not what team balancing system (which includes assigning joiners to teams) is for. If game prioritized assignments over team size balance, it would lead to horribly unbalanced scenarios in 64-player environment, especially early into assignment's life. And artificially bloated queue wait times.

I'm not saying that priority number one is to join to those servers that have the spots on the right team - that is, if you need to disarm the bomb, you should spawn on what, allies? side, but it should find the server with an available spot first, and check if this spot is on the allies team. If not - search for another available server, and so on, until the sweet spot is found and the player can complete the assignment. I mean, what is the point to use this feature to find servers if you can just list all servers and pick any, on guess. Anyways, it's hard to convince me that I'm wrong, because if I can't be sure I will complete the assigment, I don't see the point to even try to complete them. To even play, if you want.