if these problems exist, and they need to fix them first, then yes. They are legitimate reasons.

If they gave the impression that they are actively trying to fix those bugs before buffing or nerfing where buffs and nerfs need to be done, then fine. But the impression I'm getting is that because these bugs are there and are bound to occur we will try other avenue's that 'sorta' fix the issue and not go back and actually do it the right way.

Then all of a sudden we need to buff tanks because Vayne starts shitting on tanks and these bursty adcs can suddenly have the tools to deal with tanks as well.

I think we're just going to run into a difference of opinion here where neither of us will be able to see/concede to the other's point here but I'll try and put my opinion in once to see how it goes.

I believe that (and I'm more than open to being wrong here) if these bursty adc's are buffed to a point that they can deal with the hyperscaling adc's in lane tanks will still be able to withstand those bursty adc's as the game progresses. Tanks itemization is sooooo much cheaper than an adc's so unless the bursty adc's got ridiculously fed they still can deal with it.

Currently we're in a place where bursty adc's have no tools at all to deal with those tanks and they can't deal with the dps carries. And isn't that the point of taking a burst adc? You sacrifice late game power for the hopes of shutting down the enemy adc?

To touch on your point of Vayne shitting on tanks.. isn't that her design? She's a late game, true damage that scales with hp, scaling adc. Her job is to demolish tanks and provide insane dps, but her weaknesses should be the laning phase and her short range. But that laning phase weakness is practically non-existent currently.

Then bruisers are shit too.

If I ever see a meta where bruisers can't 1v1 an adc I will buy you a mystery gift. That is literally their job, and outside of outplays and missteps I never see bruisers fundamentally unable to deal with adc's. The closest time we ever got to that was in S2 but I still remember quite clearly olaf and nocturne running down adc's with abandon.