As an ADC Main...

Its not just the AS; its also that most ADC builds are actually really low AD. IE, BT, and LD are the only AD most ADCs buy in a standard triple crit build; that's 80+80+40=200 AD. The crit is there to amplify this because otherwise, their AA's wouldn't actually be doing that much damage.

Honestly, if they'd just give more AD/AS items, it would be nice. There's currently only one (BoRK) and not all ADCs can reliably use that.

I think it would be cool to bring back BT as a viable first buy again. Right now the demand to do damage early on is so high that you can't really afford to build full BT and a Zeal item as your first two like you could back in the day. But I think based on how strong burst damage is right now, it would be perfectly justified to Buff BT to the point where it is a viable first buy again. So you'd go BT, zeal item, IE or BT, zeal item, second zeal item, depending on how the matchup is going.

do not need att speed just build or

Honestly, Riot needs to fix their ill-conceived mistake of several SEASONS ago and buff armor. The mistake of long ago was changing Last Whisper to BONUS armor pen instead of total armor pen as it was originally. Apparently that JUST got put back to what it should be (total armor pen instead of BONUS armor pen) in the last few patches. Now if they can buff tanks to be what they SHOULD be "defense against BURST (assassins, mages, etc) then ADCs can go back to needing LW as a "must have" item instead of the health tree direction the game has been in for a long time. The problem is most people don't bother with LW (most of the time) because most people don't bother with bonus armor, so it was basically useless and instead EVERYONE was just building burst.

I honestly can't figure out what the heck I'm supposed to build. Four games of Tristana last night and realized on my first back that Essence Reaver was not going to work the way I was used to (no more 40% CDR perma AS boost Tristana). Tried BotRK but it was meh (was that way even when it had 55AD). Good item if you want to farm and outsustain your competition, but kind of useless if they can burst you in an all-in. Tried Death's Dance a couple times but had no attack speed (had good supports those two games which was frustrating). Went with Bloodthirster last game... which was as horrible as I remembered it being (DD is better).

I probably should have picked up Berz Boots second item over RFC. In my head I was thinking the MS was irrelevant since I was being one/two shot by everything and wanted the extra range. I'm just so used to playing Fortune that I don't realize how valuable it is to be able to get where I need to be in a timely fashion (honestly don't recall the last time I bothered with boots on Fortune with Ghostblade and Strut).

I didn't break 10K dmg in any of those games (probably never where I needed to be but also because death tends to interrupt damage dealing). Really miss having the Reaver/Zeal crit/CDR combo. Didn't need some 3 second break in laning to get a crit (Stormrazor passive). I suppose though that Stormrazor might very well be the only thing reasonable to build, since IE has no passives without crit chance and all the Zeal items cost nearly as much as Stormrazor. Could also run Ghostblade for giggles. Pretty sure the Pen build was awful on Trist. Then again, it's probably no worse than a build you'll never get close to completing.

All crit ADCs go crit first because no other build path can challenge crit if your 6 item build is ultimately going to be a crit build.

The reason they used to build BT first was because BT, when farmed, gave you a solid 100 AD for 3k gold wheras IE was 3800 gold for 80 AD and 25% crit. Then you'd see builds that didn't get IE until the fourth or last item, but there were also builds that rushed IE first. There is no such alternative now similar to that old BT.