A bit of a mix here...
The TLX might be FWD based, but most are AWD which is second to none. Its guilty of not being a TL, is all.
A TL in manual with AWD is also second to none. It's an amazing car that gets RWD at will and drifts.
An IS is RWD, has always been, and the only reason I drive a 2010 E61 and not an IS / SportCross is that I can't find an IS for $900.
The Lexus ES is indeed FWD, and it has sold like hot cakes forever. Different market.
That Acura has lost its way is an undisputable fact, but in my mind it's they never got on the right way to begin with, because of their insistence and maniacal obstination to NOT release a V8, ever - even back when it was mandatory to climb the luxury peak. I'd chart it to the general 15 years of design insanity at Honda, where there was an internal yearly championship of bland design.
Lexus is not comparable in this regard. Their stuff sells, and sells well.
You cannot make an RWD vehicle just by putting AWD and shifting torque. RWD structure is different. Acura has a transverse engine. In that category where Acura wanted to play, a transverse engine is a no-go. Period. You lost the race against weight from the get-go, as well as momentum, as the engine sits in front of the axle. You now need to pin down the front end to limit, to a certain extent, understeer. There is NO fun car with excessive understeer. And bcs. of that, comfort is compromised.
IS is RWD. But it is one that is a mixed bag. After the first generation IS, Lexus decided to abandon chasing the BMW 3 series, and make the vehicle also more attractive to their customers in retirement homes. Yes, it is a better executed vehicle by all means compared to ES, but it is still a vehicle that has balance issues, where they saved money by not shifting things to the back to get better drivability.
IS always had a lot of potential. But, as I mentioned, when I see battery under the hood, I know they were never serious about enthusiasts.
Lexus stuff sells. They have their own customer base. But IS was never an Audi or BMW competitor. There were too many compromises. Hyundai tried with the G70, and they could have gone somewhere if they had stayed committed to it, but they also chickened out.
Acura's first problem, the basic one, always was that it was a glorified Accord. Again, FWD structure is basic, the most fundamental problem when chasing BMW 3 series or 5 series. All these cars started their existence with BMW 3 series as a target. But they wanted to sell you Costco Kirkland Blended Whiskey instead of Glenfiddich 14yrs old single malt.