Monsanto is now a relatively focused company that mostly sells seeds: Many GMOs, some bred traditionally. They also now sell some services related to optimizing seed selection for a particular field. If you read their PR(which you might believe or not), there is much focus on minimizing pesticide application, and instead make the plants themselves more resistant to pests. So instead of spraying your field with a liquid full of Bacillus Thuringiensis, they'd rather have the farmer grow plants with leaves that produce the same toxins than BT does.

The market cap is just 63B. In comparison, a Walmart is 240+. The main reason they are smaller than their competitors is that they separated their biotech arm from their chemical company roots, while most of their competitors are still mainly chemical companies: BASF and DuPont. If we just compared their seed-producing operations though, Monsanto is probably larger, but it's not as if I've checked the numbers.

The thing about political influence is that it's not really about size, but about being in a position so that you do not have clear opponents. Farmers as a whole do not dislike Monsanto, or they'd not buy their seeds. They tend to lower crop prices, so it's not as if the next level in the food production chain has a problem with them either. So, as far as getting laws that are helpful to them, their one opponent is certain kinds of environmentalists. It's how lobbying works: It's easier to get a few people to spend a lot of an effort than to get a whole lot of people to do very little.

What do you mean by same thing? Monsanto has hands in many things, including software development. If you mean GMOs, which they have have become infamous for, then absolutely. Bayer, for instance, is significantly larger.