Definitely agree that Tony’s “Lifetime” should be included as one of the OP’s next steps. Tony’s singing and lyrics are pretty cheesy, but the opening track alone is worth the price of admission.Congrats on expanding your listening musical horizons!!! There are many places go from there (and elsewhere.) Sometimes it takes time to absorb denser, deeper music, nothing wrong with that. The musical tragedy would be just stopping. Some of the most obvious music has been mentioned, so I'll skip those and go a little deeper.
Older Weather Report like "Live In Tokyo." Freer, looser, w/ drummer Eric Gravatt (maybe not your thing, but as far from Heavy Weather as it gets.) "Black Market" would have been my first choice too, but "Heavy Weather" get's all the attention because of Jaco.
Larry Coryell and Eleventh House w/ Alphonse Mouzon, sort of a funkier Mahavishnu.
Also Alphonse's stuff with McCoy Tyner is jazz with a "noter fusion" influence "Enlightenment," and "Sahara" and "Focal Point" w/ Gravatt. Alphonse Mouzon "Mind Transplant" is an even funkier and rockier version of that Mahavishnu approach w guitarist Tommy Bolin.
Cobham's "Spectrum" and "Crosswinds" are both classic, and "sort of" Billy's extensions of Mahavishnu (though a little tamer.) Then there is the band "Dreams," with Cobham and the Brecker's.
An even funkier thing is the early George Duke stuff "Faces in Reflection" and "I Love the Blues, She Heard Me Cry." w/ Ndugu Chancler, I love that stuff.
A band that everyone forgets is "Fourth Way" w/ Michel Nock, Ron McCure, Michael White, and Eddie Marshall, pretty cool jazzier fusion, there is even a classic John Handy "Live" record that was sort of a precursor to Fourth Way, and is in this same vein (but with drummer Terry Clarke and Don Thompson playing FUSION!)
I really dig Narada Michael Walden's band The Warriors, there is a live record from 1983, KILLER!
When Jeff Beck and Jan Hammer first hooked up on their "Live" record with drummer Tony Smith it was a rockier version of a Mahavishnu type of thing.
Then there is Jan's "Oh Yeah?" w/ Tony Smith. Must have, ESSENTIAL!!! That might be a great nextstep!
When Jan collaborated on Steve Grossman's "Some Shapes To Come" w/ DRUMMER Don Alias, it messed people up! Again essential! That band evolved in "Stone Alliance" a trio with Jan, Gene Perla, and Don, which was a little jazzier but some of my favorite music EVER!
Santana's "Lotus" (live) was the second band moving into a fusion exploratory place. Pretty cool! And Santana and Mahavishnu John did at least one record together (not my favorite though.) Santana's "Swing of Delight" is very good though.
Stanley Clarke "S/T" is pretty essential Fusion Tony with Bill Connors (playing guitar.) Jan, and Stanley (not much space for anyone else with those four.) Great record!
Which (of course) leads into Tony Williams Lifetime (which since you hadn't heard Mahavishnu, maybe you haven't heard this.) If so, THAT is your next move!!!! "Believe It," "Million Dollar Legs." And while you are at it, how about the seeds (precursor) of Mahavishnu, Tony's Lifetime "Emergency!" Freer, and the first Jazz Rock "fusion."
Sometimes it's fun and more enjoyable to go BACKWARDS from a musical point to see how it came to be. That would involve going to back Miles' "Jack Johnson" and John's "Extrapolition," "Where Fortune Smiles" and "Devotion."
If you get this far, I might suggest the first Steps band (w/ Gadd and then Erskine.) The "Smoking at the Pit" was GREAT. And then Steve Khan "Eyewitness" w/ Steve Jordan, and The Brecker Brothers "Heavy Metal Bebop," "Detente," and "Straphangin."
Get back to me in a few years, that will set you up just fine!