MT4 vs MT5 in 2026 for algo traders — switching costs that actually matter

Still seeing brokers push MetaTrader 4 hard. MetaTrader 5 wins on multi-currency tester and real ticks.

Who fully switched? Who tried and went back?
I care about: porting MQL4→MQL5 bugs, tester parity, and whether your broker's MT5 book is worse than their MT4 book.