Not to be a homer, but the two biggest FA additions are Armstead and Hill.
Armstead before, during and after FA was the overall #1 FA to obtain, then Hill who is arguably the most dangerous offensive weapon in Football pops into the picture, and if you look at it, he was the only player dynamic and roster changing to compete with Armstead to who was the biggest addition.
In all due respect to Von Miller who was and still is one of the best pass-rushers in football, he has gone way down to the pass-rusher he used to
be. In fact if you look at the 4 worst seasons pass-rushing Miller has had, his last two years are among them, including 8 two years ago, and a not much better 9.5 last year, still good stats, but there is an obvious bit of decline, while Hill and Armstead are still playing at their top level.
Granted Armstead has an Injury issue he needs to get past, and Hill needs to rely that Tua can be at least as efficient as Mahomes was, while Miller at LB just needs to perform, Hill and Armstead each still help the team more and should be 1 and 2.