I tested out Bear Audio on some mp3s.
https://www.bearaudiotool.com/mp3-to-midi
I'll have to say, sound-wise it does a pretty good job of duplicating what you put in to it. The more complex the sound is (more things happening at once, such as singing plus drums plus multiple instruments) the more muddled it gets. But I was able to actually make out some lyrics in a few songs I tried by selecting a certain sound for it to play back with.
I haven't actually opened one of the midi files in an editor, but I imagine visually it is quite a mess.
I tested out converting a 30 second pitch slide of -12 to +12 semitones around 440 Hz. The resulting MIDI file does not pitch slide or use pitch bend. I imagine this is why you are having issues, because the vocals I assume are essentially using constant pitch bending (based on what I've heard of Indian singing before). The converter is rounding all of the pitches to the nearest semitone, so you will lose any of the in-between pitches, which are probably the exact thing you are looking for.
I attached the pitch slide mp3 and resulting pitch slide MIDI file so you can see what the converter is losing.