The OM 50-200 is an excellent lens, no doubt, but it is somewhat lessened in its legend by its own stable mates.
https://www.youtube.com/watch?v=oXmxtXnj6j0
Lots of comparisons, lots of opinions, but the consensus seems to be consistent.
Compared to the 40-150 ($1500au), 100-400 ($1600au), the 50-200 ($3500au) + the two TC’s, to make it a complete story ($750au), it is expensive, but many find it worth the outlay.
Here is what I would do.
The 40-150 f2.8 is smaller, lighter and significantly cheaper and effectively identical in real terms. The 50mm (100mm full frame equiv) loss is not really a great deal in the field and to me the slightly less capable teleconverter compatibility is also irrelevant, as will be explained below.
These shots taken on the shorter lens are too important to ignore, so a zoom is ideal to cover both.
There is cropping power, the reality that most subjects fall into short, medium or long lens territory, so a little more is rarely enough to cover all situations (hence the TC’s) and it’s black, which I prefer as it does not scream “look at me”.
These images are often a strong crop on my 300mm, so if I can add (ff) 200mm of reach and at least match the quality, then I get a larger file out of it. If the quality goes up a little, even better.
The 100-400 (f5-6.3) is the equal of the 50-200 with 2x TC (f5.6) optically as several tests have confirmed and beats it in AF performance, at about the same size and again, it is black. The problem is the almost mandatory 2x TC in a 50-200 only kit is a compromise even with a lens designed to take it. That does not change. AF is slower, resolution and contrast take a hit and the extra reach over the 1.4x is barely worth the pain compared to cropping.
They are all weather sealed.
The other advantage of the two lens kit is depth and versatility. You can use the long zoom on a tripod and have the other in hand on a second body (partially paid for with the difference in lens costs). If either met with an accident, they are cheaper to replace and the other can fill the hole for a while.
There is no mucking around with TC’s. I and others have compared my 40-150 with the TC to the kit 75-300 and they come close, which means adding more cost to a dearer lens nets nothing more than a cheaper lens designed for the job. You could still also buy the 1.4x TC for occasional use and gain even more reach (and still have a cheaper kit).
When does “little white” win out?
When you might need to take both the other two lenses at the same time and weight is an issue, the 50-200 then wins in both weight and size (but not cost), but for me, and I am only talking my use case, that would rarely be an issue as I do not climb mountains with lots of gear or if I do, I rarely need bth reach and speed.
If I need the two, I am likely using one of the other based on light and need, for example the football finals the other day, which could have been done with the long zoom for 80-90% of the time, then a switch to the 40-150 for late evening (which I basically did, even though the f4 300mm was coping fine). I could even use the 12-60 Leica on my second camera and fill the gap (24-800 in two lenses with a gradual creep from f2.8 to 6.3).
The other outlier here is the 40-150 f4, an excellent lens, really worthy of comparison to the others and a great way of taking this quality anywhere. This is my day bag lens, but deserves praise as a compelling choice in this space.
A stellar performer that has taken more good sports images than I realise.
So, me, I would go with the two lenses, or even just one if I had a more limited need.