My question is then,
(And I mean this is a fun way, not a confrontation way

)
What determines what is “necessary”? What is the standard measurement for that? Is as bassists we just need a passive DI?
Do guitarists just need (2) sounds clean & dirty? Anything more is not “necessary”?
To me “necessary” is a pretty grey area.
I’m curious how other TBers define this.
I think the distinction is between a need and a want. Need being something you require and want being something you desire. There is not necessarily a clear distinction or delineation between needs and wants...and how these terms are defined can be somewhat situational.
A passive DI may be all that you need and want. You may also need and want more. Or you may want more, but not really need it. So at some point, your wants can exceed your needs. Also, it's possible that you way not actually want what you need. Life is funny like that--The ramification is there is no such thing as a "standard measurement." We each decide for ourself.
As a bass player, we may want something specific for our tone in the mix...but often somebody else decides what the actual needs for the mix are. This is likely to be based on their needs, but also on their wants and how they disagree with our wants.
I can definitely understand that sometimes distortion or other effects can be useful with bass. But, I generally prefer more of a clean, full-range sound. So I am perfectly happy with just a DI (for recording). I assume the engineer will use whatever magical studio sweeteners he/she prefers...perhaps a preamp, compressor, or EQ.
The last recording session I was on, I was told to bring my normal amp and we spent an hour or so fussing with mic positioning. After that, the engineer fussed with resolving the phase issues between the mic and DI. I preferred and wanted the pure DI sound, but apparently that is not what was needed

...meaning I was overruled.
On stage, my amp typically serves primarily as my personal monitor, rather than as a sound source for the FOH mix. I like my bass to cut through the mayhem on stage and I want to be able to make adjustments without degrading all of the mixes derived from my DI.
I normally plug my bass straight into a quality flat DI. I used mostly stuff like: Radial J48, Radial JDI, BSS AR116, and Countryman Type 85. This was before speaker SIMs or IR loaders became common. Never had any sort of problem getting a good sound. If I was still gigging today, I would expect to do the same. If the audio tech wants to use a speaker SIM or IR loader, it's on him/her to provide it, as I feel no need to use this sort of tool (YMMV).
If I were running IEMs, I would change my approach a bit and use either an EQ such as the Empress Mk2 ParaEQ Deluxe or a preamp DI like an Tech 21 Q\Strip (these are just two examples out of a range of possibilities). The idea is I would want the ability to directly adjust how my bass sounds in my IEM mix. I would expect the audio tech to further process my signal for FOH.
I would be willing to try a speaker SIM or IR loader with IEMs, but it all honesty I feel playing through speakers causes the sound to feel laggy; meaning it cause me to feel disconnected from my bass. Speaker SIMs tend to lop of the high end which is the opposite of what I typically want. In my experience, the darker the tone, the more laggy the sound coming from the speaker feels. So I tend to use a fairly bright sound on stage to help mitigate the problem (this is what works for me and YMMV).