If anyone searching the best solution to merge Outlook data into one then I would suggest the KDETools PST Merge.
Join various PST files such as Emails, Contacts, Calendars, Notes and all.
Combine PST files in Windows and Outlook Version.
Join PST files without MS-Outlook installation.
Work within ANSI and also UNICODE formats.
Free Version is also available.
During the process, it easily removes the duplicates PST files.
Join only selected PST files or folders.
Merge PST files with particular date ranges.
More Info: https://www.kdetools.com/pst-merge.html
If you have multiple PST files and you want to merge them in one PST file, try Merge PST Tool to easily complete this task with simple mouse click. It supports both ANSI and UNICODE PST file and merge multiple PST files in one PST file without any data loss.
Visit here for more info: https://www.osttopstapp.com/pst-merge.html