Happens! At least you had fun.
The combo timing window, on d-throw is pathetically small. When I spar against my friend on his TV, it takes me 10 minutes to adjust. I'm at a level of flawless execution on my home setup. It's a handful of frames, 60ths of a second. Why the hell they made the timings so damn tight is just absurd, I agree.
Even getting the f-air to work vs. outwards DI requires a precise input of dash generally above 30%. Just looking at videos from tournaments, I think many of our best players simply forego grab combos entirely because of how tight the timings are (i.e. unreliable).
Mario's d-throw has tons of frames of leniency and doesn't require any sort of special dash input, and its knockback barely lifts the target off the floor so the impact of DI is negligible.
I think at some point they couldn't come to grips with Samus having dash combos AND grab combos, so "let's leave them in there and just make it really hard!" was the (ill inspired) design decision.
