I just don't understand what this thread is about! I mean if your Gmail is set up as IMAP then it behaves exactly the same on the iPad mail app as it does on the web.
You don't need to sync to your computer to delete mails. It depends on how you have the folder behaviour setup in settings on the iPad, but basically on an IMAP account, whatever you use to view your mails will show the same thing. In essence, if you delete an email, it will go to the Trash folder in your iPad mail app. Then, if you want to permanently delete it, go to that folder and delete it again. Otherwise, it will get deleted from the Trash according to the rules you set in Mail settings. Whatever you do, it'll be automatically synced with the Gmail server.
And you don't have to swipe each one and press the red button, you can tap edit and just select each one you want and then delete.