From my understanding, your last communication with the journal was about one week ago where you were informed that the senior editor will be reviewing your manuscript on priority. It is not uncommon for the journal review process to take 3-4 months. In cases when the manuscript is re-submitted after revisions, journal editors usually have 2 options:  They can either assess the revisions themselves and decide if they are adequate without sending it to the reviewers or  they can send the revised manuscript to the same reviewers who did the first review to check if they are satisfied with the revisions.
It is possible that your manuscript was initially sent to the same reviewers who did the first review and they were unavailable or were not able to complete the review. This could explain the delay of 4 months. After your email, the editor could have reassigned the review to a senior editor to expedite the process. Please do not worry since it has only been a week and the journal is responsive to your queries. I would recommend sending another reminder after 2 weeks requesting the process to be expedited. I would not recommend asking for a change in the senior editor since it might further delay the process. Since your manuscript is so close to getting published, it would not be advisable to withdraw and submit it to another journal as this would mean starting the complete journal evaluation process from scratch.
Since your manuscript only received minor revisions, chances of publication are high. The best thing you can do now is to be patient and follow up with the journal regularly.
- What can I do if there is a delay in the review of my revised paper?
- How long should I wait for a response from the journal?