No; priority mail is worth the price for some things to some destinations. If I ship a plant by priority mail to the west coast tomorrow, it'll likely arrive on Wednesday, unless it's going to a "special" address, such as SW OR, which seems to be a black hole of shipping. If I use 1st Class, it might and only might get there by the end of the week, after being exposed to a cross section of plant-destroying weather along the way. If time and conditions don't matter and the recipient doesn't mind, then 1st Class is fine. With Priority Mail, pay attention to weather conditions at the destination, because the final trip from the PO to the recipient can definitely be the plant's final trip if weather conditions aren't favorable. If they see a box is marked "live plant" and/or "keep out of sun", my USPS & UPS delivery people carry boxes around to a shady part of the house rather than leave them in direct afternoon sun at the front door. Not all will notice or make that extra effort.
By the way, Jim, if you aren't getting 2-day shipping on Priority Mail, ask your PO what time a package has to arrive by to get out that quickly or if there is another nearby PO that can move them quickly. As Rattler mentioned, some POs are hubs and packages tend to (but don't always) get into the system more quickly from them.