[next-gen on clould] store read query are not balanced

## Bug Report

### What did you do?
1、run tpcc workload with 32 threads, 64 threads, and 128 threads respectively

### What did you expect to see?
store read query can balance

### What did you see instead?
store read query can not balance

### What version of PD are you using (`pd-server -V`)?
sh-5.1$ ./pd-server -V
Release Version: v9.0.0-beta.2.pre-138-g5f2d4ec
Edition: Enterprise
Kernel Type: Next Generation
Git Commit Hash: https://github.com/tikv/pd/commit/5f2d4ece1a28de21bd78c3a0725c4a2954652250
Git Branch: HEAD
UTC Build Time: 2025-10-11 03:37:38
sh-5.1$

TiKV
Release Version: 8.5.0
Edition: Cloud Storage Engine
Git Commit Hash: 81b5a0b385dc4b536ad9e29f450c6658e70a6d9f
Git Commit Branch: HEAD
UTC Build Time: 2025-10-20 03:54:16
Rust Version: rustc 1.77.0-nightly (89e2160c4 2023-12-27)
Enable Features: pprof-fp jemalloc mem-profiling portable sse test-engine-kv-rocksdb test-engine-raft-raft-engine cloud-aws cloud-gcp cloud-azure
Profile: release