While enterprise customers don't represent a huge pool of customers, a few of them can lift your revenue to a whole nother level. Creating personalizations for enterprises using firmographic segmentation is worthwhile if done well.
Startups represent a large audience and while they may not have the purchasing power of a Fortune 500 company, they still control a lot of the word of mouth and influence related to products and services. Targeting startups is easy with firmographic segmentation using a revenue range and founding year.
Most B2B companies can't sell to target customers of all sizes (the exception to the rule being companies like Intercom and Hubspot). The reason behind it is simply how the sales are organized in the company. If you do want to target customers of any size, make sure your sales is aligned to the size of the target customer and you're using proper firmographic segmentation.