Is which red or white oak? Is the bottom one your floors? Your finisher needs to make you samples on your floor as others pictures and monitor images will be necessarily be true or how yours will look in your home. He needs to make you samples as that is all part of the process you hired him and are paying him to do.

If your flooring guy cannot do samples on your floor get a new guy. I never want the flooring guy choosing the stain but they need to do samples on your flooring after sanding . If at all possiblein a closet so they can play a bit without messing up the whole floor.

"considering medium brown/weathered oak

chesnut/weathered oak"

Isn't that what is in your second photo? You say "my flooring guy is pretty useless coming up with combos on his own", but it looks like your second photo shows he is providing what you are asking for. Your top photo is not "medium brown/weathered oak/chestnut". I think the flooring guy is giving you what you asked for, but what you asked for is not what you actually want. Show him your top photo that you posted here.

Here are photos of chestnut stain on white oak and weathered oak stain on white oak (a much more gray finish than it sounds like you want). So you need to give your flooring guy the correct instruction of what you want, and not blame him when you do not.

Samples cost time and money.

Time and money that the cheapo guys will not spend. Those are grind production in and out guys. Not professional consultants.

There is a test for determining the kind of oak you have. See this discussion.

https://www.houzz.com/discussions/6283008/is-this-floor-sufficiently-blended

Stop, don't be pressured to make a decision. Go slowly. Be clear on what you want and show photos so the installer isn't guessing.

2-4 standard colors is fine. More than 4 colors, along with custom colors. Clients would need to pay for materials and labor. Client keeps all material paid for.

Quality flooring stains (Bona) now cost $20 per quart. Client would need to pick up bill for colors.

Should he be testing them on my floor though and not just sample boards? I’ve asked twice now and he doesn’t directly answer no he won’t he just makes the sample planks but I really don’t feel comfortable making the final decision without testing on the floor.