One of the biggest flaws is that due to its poor bulk is that it struggles to switch in to things without being crippled a fair bit, especially in terms of Special bulk. If your opponent can play well it is hard to switch Crawdaunt in on something unless they lose a Pokemon.
It's second problem is that it is really slow and easy to revenge kill, even at +1 speed from a DD boost there are quite a few common UU Pokemon that still outspeed, including Raikou, Mega-Manec and a lot of Scarfers which can easily OHKO it.
Now I am not about to argue that Crawdaunt doesn't often pull its wait, because it does have rather strong consistency, though it doesn't always pull its wait if the opponent can predict well (still is a very strong poke though). I also believe that we should be arguing that its most broken role on a team is that of a Wall-breaking, hole-punching, hard-hitting monster, not so much of a sweeper as if you are getting 6-0ed just by a Crawdaunt then there is something seriously wrong with your team-building.
Now considering there is a bit of a comparison between Magnezone and Crawdaunt I feel like we should have a closer look at the differences between the 2.
Points in favour of Magnezone:
• Better bulk and Defensive typing granting better switch in opportunities and harder to revenge kill
• Volt Switch for momentum
• Better speed capable of outspeeding more threats and some potential to run scarf
• Better overall neutral coverage between STABs (less Pokemon in UU can resist both types)
• Has another option to Analytic in Magnet Pull which can catch people out, Crawdaunt should only run Adaptability.
Points in favour of Crawdaunt:
• Boosting moves to better setup a potential sweep
• Powerful priority (probably its best advantage)
• Added crippling utility in Knock Off
• Switcheroo
• Better coverage options