So I'm relatively tall, long arms, have always had an over-the-top move and in generally my swing is pretty vertical. When I started playing competitive golf I ran into a handful of teaching pros that gave me unsolicited advice, usually at country clubs and usually just a 2 minute snap judgment. Most of them were some variation of "oh, you have to keep your feet planted on the ground, keep both legs bent don't straighten your left leg, swing around your body and lay it off more, rotate your hands more, etc." While I never really tried to make drastic changes, occasionally I'd video my swing trying some of those changes and always noted two things - first, it always felt insanely unnatural. Second, on video they were not nearly as drastic as they felt. So I kinda just accepted that my swing was garbage and at some point I'd have to do something drastic if I wanted to really improve.
Then I was at a fitting with a guy who's now running all the fittings at TPC Sawgrass, but at the time wasn't that big a deal. I mentioned that I knew my swing was trash and I had an over the top move, but that I just wanted to get fit into clubs that would help me score, and that I'd fix things later (ie., focus on the clubs and don't try to correct my swing during a fitting). He'd been working with some of the early folks focusing on biomechanics and the golf swing, and immediately rattled off 3 or 4 guys who had similar builds and similar tendencies on tour, 20 guys who got on their toes a bit (or a lot) during their swing, etc. Said he'd tweak some things but honestly wouldn't change my swing much at all based on the numbers. Around the same time a few pros, I remember Sergio was one, Stenson maybe, and a couple other lesser-known guys had just abandoned "fixing" their swings from being too vertical, too laid off, etc. mostly focusing on biomechanics.
I gave up on chasing a perfect swing, focused on consistency, the mental game, short game, quit changing clubs - went from maybe an 8 at the time and got it down to scratch. Not that I don't still tweak and work on correcting my bad tendencies, but I'm in my 40's and I'm not sure how realistic it even would be to retool my swing. I've seen plenty of buddies try it, and unless they have serious swing problems and have never broken 80, I've seen roughly a 0% positive outcome from them.
All that to say - I'd be extremely careful going with a "complete overhaul" approach to a golf swing if you're decent and have been playing for a long time. I'd also be extremely skeptical of teaching pros who recommend that approach - there's a lot of money to be made spending a couple years making a decent golfer awful then decent again.