I didn't want to make the Link paragraph too long, but yes the remote bombs are great. So is the bow and arrow. And the up special. I feel like link doesn't have a single bad move in his arsenal.
In the tips section of the game it said that projectiles that deal 50% or more damage cannot be reflected. Maybe the game's tooltip is wrong though, I haven't tested it. Samus' spike just lacks range IMO. Either that or I'm just bad at using it. Link's spike seems easy because it stays out forever, so timing isn't an issue. Do most moves just whiff when people are lying on the ground then? I just found out that there are up tilts, down tilts, and forward tilts. How do you do these? So far I've only figured out how to do a down tilt.
You do forward and up tilts exactly how you do down tilts, by pressing holding in a direction and pressing A. Alternatively, you could switch your right stick to tilt attacks to do them instantly with ease, and just do smash attacks the normal way. As for moves whiffing when an opponent is on the ground, it's quite logical - you gotta hit the ground if that's where they are, and most moves don't.
Link's down air does stay out for a very long time, but it only really spikes near the beginning. True, even the post-spike part of it can still be amazing for killing as it connects into an up B (or at least it did in Smash 4, not sure about Ultimate), but technically the spike isn't out forever. Samus' spike takes some getting used to, but once you do it's pretty easy to land as it covers a very wide area below her.
The tips section of the game isn't wrong about 50% projectiles bypassing reflectors, but no projectile does has that much base damage as far as I know, certainly not Samus' charge shot. You only reach damage outputs that high by reflecting projectiles multiple times.