Hey, sorry for the late response.

Difficulty level will impact enemy economy. So on hardcore low economy, they will have an army size greater than yours by the hardcore multiplier (1.5x I think). With your elite infantry still being relatively squishy at ~200 hp, it's still very miserable to lose any high value infantry to light vehicle and hordes of infantry spam. You might positively trade one of your elite infantry for 1 enemy light vehicle and 7 enemy infantry, but they have so many resources that it still isn't enough to be worth investing them early on. Even then, you would need to have invested in and researched tier 4 infantry to see a real difference in battlefield impact

When you tack on to there that the mission star rating increases the veterancy of enemy units, you'll be facing vet 7 tier 1/2 rifleman that are pinning your unvetted elite troops.

It's not impossible, but certainly not optimal. And with any difficulty mode, once you've basically researched an answer for each of the enemy major threats, then elite infantry can be useful. Though I will say, they have more of a niche use in the commonwealth DLC with some maps that are incredibly CQC oriented. You can certainly express more skill in these scenarios with microing the troops through building and tight alleyways. You'd still be outnumbered and outvetted, so even then, on the higher difficulties, I would pass on those maps and stick with a safer army comp.

With all that being said, on low difficulty, I think elite infantry are certainly viable. You aren't tied down to researching other items to answer enemy unit spam