The problem being you've named four moves, whereas almost all Excadrill run SD with three moves. Two of these will always be EQ and Rock Slide, so once you've found out its last coverage move, it's just a matter of switching in the appropriate counter to that set.
Yes I have named four moves aside from SD, that's why I said X-scizzor 'OR' Return, I did not expect it to have both.
Anyway, the problematic issue here is that in order to find out what move set Excadrill has, it may cost you a Pokemon - Excadrill will be only using its non stab moves as a last resort so in order to find out if it has X-scizzor or return, you would need to switch into something like Celebi. If Excadrill then uses X-scizzor your Celebi is screwed unless you switched again. Additionally, should Excadrill meet something that it cannot handle effectively, it only requires a simple switch (it's not likely to die from SR/ Toxic Spikes damage), until the threat is dealt with.
Furthermore like I said, Excadrill will be hitting almost everything hard in OU. I've just checked and the only Pokemon resistant to ground typing wise (excludes levitate), that Excadrill won't be able to hit super effectively are Landordus (ground/flying like Gliscor), Skamory (Steel/Flying), and Fighting/Grass Pokemon (i.e Breeloom and Virizion).
Admittedly, why are people so worried about Excadrill? People can say to use a Choice Scarf to deal with Thundurus, so why can't people say to use a priority user to deal with Excadrill? There's plenty out there: Conkeldurr, Azumarill, Hitmontop, etc.
"Priority i.e aqua jet Azumarill can revenge kill Excadrill (if it decides to stay in) however it will be 2KO’d by Excadrill’s EQ, therefore you only have one shot to switch in and aqua jet if you don’t plan on sacrificing another Pokemon. That being said, I’ve never seen Azumarill in OU and Azumarill would also need to carry choice band for the OHKO on Excadrill therefore making a predicted safe switch even easier. Conkeldurr on average will be 2KO’d by EQ (or OK’d with +1 SD) and it cannot OHKO Excadrill with mach punch even with iron fist ability."
As for Hitmontop fair enough, but given the fact that people with Excadrill may worry about priority from Conkledurr, there is bound to be some sort of safe switch in their team i.e to Gliscor or Skarmory.
I don't get it, but Excadrill has rarely been a problem for me. Its defenses are shit as hell(lol Escavalier does 60% with unboosted Megahorn)
If it's defences are so 'shit' I wonder why it can live crucial hits such as Max Att Conkeldurrs mach punch even with iron fist ability.