ASM3 is going to take something momentous to regain the former Spidey glory.
MCU, more superhero movies in general, franchise fatique. Spidey has a mountain to claim with the 3rd movie.
Skyfall turned around the disappointing QoS (putting it mildly I thought that movie was a PoS) so it's not impossible. But despite largely the same cast as QoS, in it's favor Skyfall had;
1) Oscar winning director (I think).
2) Arguably THE best cinematographer in the business.
3) A brilliant script writer.
4) A big gap between QoS and Skyfall (allowing the dust to settle often is a big help)
5) Less spy movies in direct competition
None of which will happen for ASM3.