Brett, to be fair to ESRI, MS Access, does have a 64bit flavor, does not perform well when the data is closing in on the Gigabyte data range and starts performing worse and worse as the data size increase. However, in day to day practice, work from start to finish, speed is not measured by the efficiency of the data base alone, it includes preparation, communication with other software, conversions, cleaning, data accessibility, post operations and finally completion. The efficiency of your database is important but in a lot cases that is negligible. What access gives a user is ungodly compatibility with almost EVERYTHING so in most cases other than the data speed (which is only a small percentage of the work effort)...you will be spending enormous amount of time and extra work to get data into the system, overhead management of the large databases, or file geodatabase, now have to export that data out to format other applications can read, for example, for reporting I use crystal reports, I know that product cannot read a file geodatabase, so right there is an additional step I would have to make exporting the data into a format that can be read. While it is true, MSACCESS geodatabase is inefficient with large datasets, my point is that the Pre and Post time savings using Access far overwhelms it slowness in geo-processing.
Please do vote: Enable ArcGIS Pro to access ESRI Personal Geodatabases
