A previous chop would also explain that change in the trunk that looks somewhat like a graft union.
Oaks are generally good at new buds on bare wood, especially when all growth is removed, so chop is a good option. Not sure how burr oak responds to time of chop but it should still be early enough in summer to get new shoots this year.
I stopped growing single trunks to thickness before pruning many years ago. The trunk thickening may be quicker but the subsequent healing of large scars and regrowing new leader and canopy takes many years and negates any time saving IMHO.
I get a much better result and little difference in timeline by regular prune and grow cycles.
Grow trees however you want. Just my 2c worth