Lots of AUv3 MIDI generators + MIDI processors on iOS/iPadOS for use with DC-coupled audio interfaces or MIDI>CV/Gate converters.
Modular-style/algorithmic/sequence your sequencers/modulate your modulators in an AU host like AUM or apeMatrix:
CoVariant MIDI>CV/Gate converter
Mozaic build-your-own MIDI sequencers + processors + Patch Storage
Drambo + Patch Storage
miRack/VCV Rack + Patch Storage
Rozeta MIDI sequencers + processors suite
Victor Porof MIDI sequencer + processors suite
Pagefall MIDI sequencers + processors
Arthur Kerns MIDI sequencers + processors
Cem Olcay MIDI sequencers + processors
Anthony Saunders MIDI recorder + processors
Laurent Colson MIDI sequencers + processors
Audeonic MIDI sequencers + processors
Aphelian
cykle de-coupled step sequencer
Riffer
Thesys
Octachron
Difficult for me to justify buying digital hardware synths + FX when Sugar Bytes, apeSoft, Amazing Noises, Ryouta Kira, IceWorks, Alexander Zolotov, Dmitrij Pavlov, Erik Sigth, KV331, VirSyn, Imaginando, iMusicAlbum, Spacecraft Granular, Synclavier, CMI Fairlight, Mutable Ins ports, Drambo + Patch Storage, miRack/VCV Rack + Patch Storage, Audulus, Zmors Modular, Eventide, Audio Damage, FabFilter, ToneBoosters, FAC, K-Devices, etc. exist.
AUv3 lists are here. Lots of free stuff too. And apps that can load PD Vanilla patches, etc.
Multi-channel audio+MIDI interfaces with DC-coupled I/O are fairly inexpensive these days, as are MIDI controllers.