Problem with this is that you are breaking the consistency, it's the same pitfall LS lineup is now running into. If they wanted to maintain the sales to reflect 2007 they should have released current or similar LS back in 2013 not 2018. They will have a hard time to build up the sales numbers with current LS cause most of the customers have left for another brand. With GS it's just going to get worse, they went from 3rd best selling premium midsize car to few units above Q70, you don't recover from that overnight. You recover from that in two model generations if you are lucky, like A6. Same fate is waiting for IS as well unfortunately, that poor thing will not go back to 3,000 units anytime soon.
Lexus is experiencing sudden death with RWD cars not because cars are not popular (tell that to Germans and Genesis) but most likely because they do not have sufficient funds or manpower to develop RWD platform products and Toyota reskins at the same time. I've said it before many times company like Lexus cannot afford to have a decision vote if they are going to develop RX-L or RC convertible, that's something Jaguar has to deal with not Toyota. If you are Toyota you build both and you build them right away. Otherwise you end up seeing your 3 year old RC plummet to under 200 units while Infiniti is selling 4 times as much and Audi is selling 9 times as much. Excuse that coupes are not popular anymore won't fly.
problem is that you are factually wrong:
1. Sedan and Coupes are overall dropping sales heavily. It is objective stats, not something imaginary.
2. Every company, including the richest one in the world (TMC), has to focus on something. Lexus chose to focus on what sells - ie SUVs. If anything, they should have done that earlier.
Growth has to come organic. Lexus has added RC, LC, NX, UX in past 3 years. Thats 4 completely new model additions to the brand. Now they sell CT, UX, NX, IS, ES, RC, GS, LS, LC, RX, GX, LX. Thats 12 model lineup.
Lexus can not have the most models, most engines, most options, freshest lineup in every category, phev, ev, petrol, diesel, mild 12v, mild 48v hybrids, full hybrids all together in every model and beat everyone in everything including 1, 2, 3, 4, 5, 6, 7, X1, X2, X3, X4, X5, X6, X7, A/B/C/E/S and billion others. They cant compete with everything anyone ever put out.
If sedans are doing bad for Lexus compared to BMW & MB, then BMW & MBV SUVs are doing horribly against what is essentially a small player worldwide - Lexus. RX alone can outsell 5 models from german trio. NX kicked butt from the moment it appeared. LX has no competition at all, its sales better than LS for many years - BMW or Audi dont even have such vehicle, MB's is old and outsold in all the important markets. UX is likely going to become bestseller from the moment it arrives.
Lexus does not need to sell GS, IS and RC at any cost. They should focus on what market wants.
As to the LS, I think people in this thread have to realize that this is few days of sales for LS.