All the good players play with controllers.
Tl;dr version: Not all of them do, regardless of the game.
Long versionThere are people that can play well at shmups in general with a keyboard, such as Prometheus (guy on shmups.system11.org w). He's likely not a touhou player, but he's one of the higher-ranking (highest that speaks english iirc) players in Dodonpachi at the very least.
Whichever controler you pick, remember that MrMonkeyMan (Higher-ranking player, not on MoTK) has proved you can destroy a difficult [STG] with a crazy score using a pad and [PROMETHEUS] proved you can do that using a keyboard. If you've been playing other competitive games with a pad or keyboard before, then you could stick with that input as you already are familiar and skilled at using it quickly and accurately. Just don't listen to the crowd of people who sing together how STGs are meant to be played with arcade sticks so arcade sticks have to be the best at it. They are wrong.
(Edited slightly for context and made more broad)
Even more to disprove your point a tiny bit is the next paragraph in which is said:
I personnally secretly believe keyboards are actually a superior input to arcade sticks. (...) That's because they're much faster at changing directions, and they're also better at tapping one direction very shortly multiple times, which are very useful perks for STGs. Some people will point to you its easier and more intuitive to make circles with an arcade stick, but that's pretty much useless !! I might be wrong about keyboard being superior, (...) [but] keyboards rule anyway.
I realize this comment isn't touhou-related, but this kind of thing applies to any shmup anyway, which is the topic matter. Just saying that in case someone wants to disregard my point for not mentioning a 2hu player.
Heck, as imprecise as an arcade stick is, if you can get good with it, it's your call.
Full Extent of the Jam, written by ProMetheus, is a good source because it presents useful tips that can help newer players get accustomed to the genre of shmups, which applies to Touhou. It may not be touhou-related, but it's certainly helpful and should be mentioned over here. The only problem is that it discusses the use of things that are prohibited discussion on this site as it is aimed towards shmups running on mame, but most of the tips that apply generally to all shmups will apply to touhou. For reference on who prometheus is, ProMetheus is a player whom of which has dominated the
DoDonPachi scoreboard, the second-highest score being almost 200 million points below him (which is like 40%-ish w)
Sorry if it sounds like I'm sperging out, but I just needed to make this point. If it's such a problem that I cited a document written by someone who knows what they're doing, feel free to tell me.