My memory isn't the best so please forgive me if I'm saying anything wrong here, but I did wanna give my take.
I think this is a good point but it's not really the same between ORAS and BDSP. ORAS was made before Sun and Moon, which was the game that took out HMs in favour of Ride Pokemon. Anything before that still used HMs, including X and Y. Since ORAS was built pretty much in the same way as XY, HMs were still the norm. This is our first remake since HMs have been phased out, so I think it's less likely we'll be using them for the sole reason that ORAS did.
For me, personally I hope they're aware that DP is the game notorious for having lots of HMs and having them be pretty bad (Plentiful uses of Rock Smash, awful surfing speed, hell the west end of Route 226 requires several uses of Rock Climb to even pass through) and if any game needs them phased out, it's DP. A big hope I think I share with a lot of people is the games will be sped up, and remakes are the perfect time to introduce quality of life changes like that.
That's more what I want and not what I think will actually happen.
...To be honest, I think they'd care more about being faithful to the originals than greasing the wheels, so unfortunately while I hate to admit it, I think it is likely we'll see continued HM usage in BDSP.
You are 100% correct. I had forgotten we didn't stop using HMs till Sun and Moon, and we very sparsely used them in Unova and Kalos. However we did still require them a lot in ORAS.
That being said, I think that is the very reason we will be using HMs. Because they were required so much in Sinnoh. Because this is just a remake of a game with already established routes and what not, we will probably still need HMs. I think it would be hard to incorporate anything that isn't HMs without changing the entire game.
Let's Go you could argue used Pika/Eevee Powers instead, however, Let's Go was a completely new game. There was barely anything the same as it was in Red and Blue. It was completely remade. Technically it isn't even the same game since in that game, it is canon the Red, Blue and Green all had already done their journeys.
Unova, Kalos, Alola, and Galar were all built with that in mind, so they were built to require very few HMs or none at all. ORAS was already established, so they couldn't really change it, which is why we needed HMs so much compared to Unova and Kalos.
With them saying size and stuff was all kept in mind, I don't think there is much they can do unless they rebuilt the entire game like with Let's Go. If they did rebuilt the game, which I don't think they did, then I'd me more inclined to believe that there would be no HMs.
That being said, I think having ride pokemon in Legends is for that exact reason. They built the game with the idea of no HMs in mind.