I disagree,back then when i tried my first boss ever,that was Brock and he destroyed me,i was like "damn,okay they are strong i need a better team",i was happy and it was satisfying to finally win against him.
Later i was able to beat all the Medium Boss i wanted with a classic stall team that required me time to hunt/money to buy,i was happy and it was satisfying too to finally be able to do my boss runs,and sometimes we have to change our team a little bit against some boss and that's good.
Now i'm thinking about a Hard Boss Strategy,i know that there are known strategies out there,but i want to try my own and see if it works,so no,to me boss are very well designed and challenging,they are one of the final PvE Content,they MUST hit like trucks,have powerful items,have a lot of iv and ev,have 5 or 6 moves,have mega and on and on,a boss that is weak or half-strong isn't interesting at all,we MUST come with a strategy to win,that's the point.
The fact that boss can switch pokes now is also good,before that we could set up easily and win on them.
There is something that i noticed,it seems like boss crits us a lot and haxx us a lot,i think that's a troll by the devs.
If we needed a specific team for each boss,yeah I would have agreed with you on the boring and tedious thing.