Wait, you're saying that if you prepare for the counters of your playstyle you might actually build a good team? SURELY NOT!
Drought Sweeper are easily stopped by Snover. Switch in on a Solarbeam and KO with Blizzard, because the sweeper is essentially trapped. Same with Swablu and Lickitung. Realistically, Drought sweepers are so easy to counter it's not funny. Hell, you don't even have to run any of those Pokemon to beat Drought. If you build a good team, where you actually consider Drought whilst making it, Drought is not a threat at all. Dokkora, for example, runs right through most Sun sweepers.
Drought sweepers are not stopped by Snover at all. Pretty much ever sun team pokemon has a fire attack of some sort, and Snover is not going to want to switch into any of those. Snover is pretty much a free switch in for any fire type (including Vulpix) who can maim it, then continue sweeping. Swablu may have its uses in stopping sun teams, but it's not going to be able to take boosted attacks from Growth sweepers and has pretty much no use outside of countering sun. Lickitung has its uses, but I'm not going to put six Lickitungs on my team. The part about sun being so easy to counter is just wrong. I'm sorry, but there are no switch ins, no pokemon that outspeed, and no survivors. And Dokkora won't have such an easy time using Mach Punch against Poison types like Bellsprout, and won't like taking a +2 Solarbeam to the face afterwards. I've said this before: Evo Stone Bellsprout has the following boosts after just one Growth: +2 Atk, +1 Def, +2 SAtk, +1 SDef, +2 Spe. Now stack that on top of a STAB 120 BP move, healing with Giga Drain, and boosted Hidden Power Fires.
Deepseatooth was broken last gen because nothing could take the hits. Now, with evolution stone, it is far less threatening, even with Shell Break. Clamperl lacks priority, it fairly frail, even with evo stone and isnt very fast. Additionally, it also has to find time to actually set up... Which isnt the easiest thing in the world.
You're right, nothing could take the Deepseatooth hits last gen, and the Evo Stone is a great answer to that. But GF also introduced Shell Smash. So although the Evo Stone kind of cancels out the Deepseatooth, Shell Smash gives it a whole new face. Deepseatooth and Shell Smash can't be on the same set. I'll show you these boosts again: After one Shell Smash, Clamperl gets +2 Atk, -1 Def, +2 SAtk, -1 SDef, and +2 Spe. After a Shell Smash with a Deepseatooth, the entire SAtk stat is doubled, making it +2 Atk, -1 Def, +6 SAtk, -1 SDef, and +2 Spe. That's like using a Special Belly Drum and Agility in one turn.
EDIT: In terms of Murkrow, I know it seems wierd but I have always thought of Murkrow not to be just one Pokemon, but several, kinda like Arceus in Ubers. Sure, it's pretty diverse and has loads of different options, but all of its sets have multiple counters, you just need to be imaginative. You also have six slots on your team...
Smash is right. You can't just tell what set Murkrow is going to run until you're already dead. Being imaginative isn't quite going to cut it. One Murkrow set has already killed half my team by the time I can send in the proper counter. And there is no perfect Murkrow counter, no pokemon can take on every type of set. I may have six slots on my team, but I'm not going to dedicate every single one to a counter to a different Murkrow set. I mean you could, and you'd be really prepared if you encountered a Murkrow, but any other pokemon could murder your team. So there's no way to perfectly counter Murkrow, and there's no way to stop it until it's too late.