Numbers were not already dropping prior to them making Jinder Mahal Champion. He was Champion for 25 weeks:go-away heat is not a real concept anymore. and the idea that Jinder's reign drove away a bunch of fans is something people want to be true, but it isn't. Ratings didn't significantly change, and house show numbers on SD were doing better than RAW at the time, which means he was drawing better than Seth on the B show. go look up the numbers.
the real heat / go away heat argument is just a way for certain fans to justify why the people they prefer are ones everyone should be enjoying and vice versa. A heel isn't a good heel because you respect them as a performer and want to secretly cheer for them. Heels of the past were legit hated and even got death threats from audience members or physically assaulted. The idea IS for people to hate you if you're staying true to your character. and Mohomad Hassan was legit hated by people, not booed but they secretly respected and adored him. I used to despise Corbin for example but I can actually enjoy him as a heel now considering most heels these days aren't that good at being heels.
and if he was really getting "go away heat" in the manner people wish was true, the numbers would have significantly dropped and that isn't what happened. numbers were already dropping prior to that, and as I said earlier, SD was continuing to pull better numbers than RAW despite being the B show at the time. even when Roman was getting this "go away heat" it didn't mean fans were completely tuning out and didn't want to see him. Roman was still drawing a big reaction even if it wasn't the reaction WWE wanted because of how forced his babyface push was and that's the same situation with Jinder's forced push as champion. That isn't "go away heat", it's just heat.
Average Smackdown viewership 25 weeks prior to Jinder Mahal winning the Championship: 2,604,760
Average Smackdown viewership during Jinder's 25 week title reign: 2,476,880
Average Smackdown viewership for the 25 weeks after Jinder's Reign: 2,618,240
He literally lost viewership during his reign and they all returned after they finally took the belt off of him.
But even ignoring numbers. Comparing heels now to heels of the past makes no sense. Heels of the past were hated because people literally believed that the product was real. Fans don't care at all about the characters themselves anymore, they tune in to watch good matches and hear good promo's and then hope that the guy they like the most gets pushed. It sucks that it has become that way, but that is how the product is viewed now. Everybody knows the product is fake, so they really don't care what character that person is playing. People Boo'd because they hated the booking decision, they didn't care one bit about the character that Jinder was playing, they cared that he was in the way of watching people they actually liked.
In modern wrestling there is no such thing as heels and faces because the audience doesn't think the product is real and don't watch it in the same way. That is why heels always get cheered and babyfaces always get boo'd. WWE never adapting to this new reality is why their product has failed so bad the last decade. People were booing Vince, not Mahal because everyone knew it was a ridiculous decision to put the title on a jobber just to appease the Indian market, which he failed at miserably by the way.