I have no clue what the consensus is, but at least in my personal opinion if the game itself lets you do it then have the heck at it. You didn't hack or bug out the game to get the stuff? Then you're playing the game as designed. Any further posturing about what is and isn't good form is just nitpicking at that point.
I myself am fully planning on jumping between saves at will now that 1.4 is out. Made it up to the Mechanical Bosses on Expert on my PC and had to let the save sit because the Twins were roughing me up like crazy and the control scheme was handicapping me, then beat Expert on my Switch when it eventually got ported there by using a little bit of cheesing at the last stretch. Now that Master Mode is a thing? Forget it, I'm not hurting myself anymore. I'll just jump between my existing saves, Classic saves, and Master Mode saves at will. I'm not hurting myself any more.
Think of it this way. You're still beating the game's full progression at least once. Expert and Master were added because people who like more challenge than the game was originally designed with weren't satisfied. Even if you can go back and sweep early game Expert or Master Mode bosses with hardmode gear like I'm doing, beating the endgame bosses is going to be just as impressive if you walk in with full endgame gear from a Classic save as it would be using nearly endgame gear from the Expert or Master Mode save. Trust me, the endgame gear on my Switch Expert game didn't make fighting the truly challenging stuff much easier. So do what you feel like, and at the end of the day, one way or another, the accomplishment is still yours.