Tyreek's speed and Kelce top 3 tight end. Can't really deny those, top talent for sure. But all the other offensive weapons are replaceable. Mecole Hardman is still developing, he is only going to get better. But right now, he is the special teams guy and they throw him in every once in a while. He hasn't been fully unleashed yet.
It is true that the Chiefs will lose cap room with the contract extension on Mahomes. But it is also true that many athletes in the NFL want to win a superbowl and be a champion. Some will be willing to get paid less to play for a team that has a chance to win and a chance for them to have more success and raise their stock. There are also many talented weapons out there who aren't being utilized properly and their stock drops because of it. For example, the former Dolphin Running backs (Damien Williams and Kenyan Drake). Once they left Miami, they showed what they were really capable of. Damien Williams has shined under Mahomes. Kenyan Drake who was always overlooked has played much better under Kyler Murray and has taken the starting job from David Johnson. John Brown is the go to guy for the Bills now,. You look at the history with the Patriots, a lot of really good veteran players have went there and have taken a pay cut to play for them and a chance to win. When you play for a great QB like a Brady or Mahomes, you have a chance winning a super bowl, having a good season, and raising your stock so you can get a bigger contract next go around. Mahomes will eat up a lot of that cap but there will be players who will be willing to take a pay cut to play for them.
As you said, It will be interesting to see how the Chiefs fill those gaps. I thought Kareem Hunt was going to be irreplaceable but that turned out okay. There are guys out there who would be big stars with a great QB. For example, John Ross would probably be somewhere between Mecole Hardman and Tyreek Hill if he was catching for Mahomes.