C-41 color negative and E-6 slides (positive) are Kodak standards. So if a lab is exactly reproducing it to these specs the color work is perfect.
However in B&W there is no standard. In fact you have to make your own standard. A regular film exposed on box speed in a general purpose developer is maybe 90% OK. And most people are then satisfied about the end result.
However if you are going to push or pull you have already to know exactly what you are doing. A normal lab can not handle this in the right way.
In principle Tri-X 400 is a flexible film which can be used between iso 200-1600 but iso 1600 and 35mm need an excellent combo film-developer otherwise you will get the crap which you have now.
My suggestion: Expose on iso 320-400 and let the lab do their regular B&W developer. Anything else: You have to do it yourself. No rocket science but you need some experiences with it which takes time and effort and a good notebook (on paper then I mean, what you have done in exposure and what you have done in development).
What I am doing for multiple different exposure on one roll and different developing times: For each different step I put a small sticker on the film surface: Camera on B, lock it, remove the lens and put the sticker on the film surface. One extra blanc picture and a next serie of different exposures. You have no mirror on a MP so if the curtain stays open, not a problem. BTW I have a M7 (Leica). When putting the film on a reel and developing tank, you can feel the sticker on the film and there you can cut it and the next part of the film on another reel and tank. Make notes what is what. In this way I have enough of one film (135-36) to do a complete film test with a developer on different developing times and exposures. When doing this on a grey chart in combination with a test chart, it is all what you need.
Here an example of the Fomapan 200 film: E.I. 100 and developed in Windisch W665 an ultra fine grain type developer. M7+Summicron F/2,0-50mm.
I am almost 100% nobody used this combination so searching the web: NO info.
The grain is neglectible and a nice grey tonal range from White to deep Black.
FP200 E.I. 100 in W665 1+0 9:45 minutes at 20,0C.