Considering the whole "Xbox trending in Japan thanks to Sakurai" & the boost of exposure DQ11 got....yeah, Smash helps get other games noticed.
The whole Byleth discussion was on point, especially the comparison of the last characters to be revealed being Ken & Incineroar. If Byleth was the first character for the 2nd pass, it might've not been as strong of a backlash because people would probably think "okay, the first pass was all 3rd party, now it's time for the 1st party stuff". Especially when the previous 4 were 3rd party, and after outta nowhere characters like Joker & Banjo, people got their expectations high on thinking they were saving the best for last.
Also if you count Roy since he was DLC in Wii U/3DS, this will be the THIRD FE character that's DLC. That probably doesn't help.
...Fire Emblem: Three DLCs.