It was controversial from the start. I recall the adults all talking about it and it was very polarizing.
I get it as to what they were trying to do but it just kind of missed the mark. I think the greatest issue was the size of the car. It was trying to pull off a look a much taller and longer car used and it just did not work as well here and even on the Imperial and Lincoln.
I will not say they were bad but they just never really connected with the market. Today they are special because they are different and that is often what leads to a class. Anyone say Daytona?
In my 20/20 hindsight alternate world, in 1975 Lasalle would have become a sub-brand sold at Cadillac dealers (as was the original). It would have basically been the Seville, but with a more sporting nature. No fake wires, instead aluminum rims that looked like wires (which did exist in the era's aftermarket). Luxury-oriented bucket seats with a useful console. Think of something between mid-70s BMWs that looked like metal toolboxes and mid-70s Jaguar that won't start. Better styling, GM reliability.
The LaSalle sub-brand would have been a good way to experiment with moving a luxury car more towards the sporty/euro end of the scale without alienating traditional buyers. Just enough "history" to give it gravitas. Ads could have featured vintage sporty LaSalle roadsters, etc. Cadillac could have continued with more dignified sedans and body-on-frame models (for easy limo conversions). Phase out Eldorado by '78 and tweak the '79 Eldo from this world into the LaSalle "Model 80x" or something. We would have been spared the Cimarron and Catera, but they might have worked as LaSalle offerings. Yuppies could have driven a sport/luxury sedan without the indignity being seen in a Pontiac dealer with all that ribbed plastic. Cadillac's wouldn't have built all those downsized FWD offerings and could have moved towards S-Class territory instead. Smaller volumes, more profit.